Image source, Getty Images

How do you track war crimes and build a case against those responsible?

The answer to those questions have changed dramatically in recent years as online posts document so much of what happens on the ground in war.

Open-source information - such as photos that are freely available to anyone online - have "completely transformed our way of knowing about human rights violations", one expert says.

"We're seeing increasingly the UN commissions of inquiry, fact-finding missions, even the International Criminal Court in the Hague, using this kind of evidence," she explained.

Read more about what experts say is a radical change in how cases are built.

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Following the news that Russia has given Ukraine's fighters in Mariupol hours to lay down their arms, what has Ukraine said about the fate of the city?On Saturday, Ukraine's President Volodymyr Zelensky acknowledged that Ukrainian forces held control of just a small portion of Mariupol, saying his government was in daily contact with those defenders.

The situation was extremely severe, Reuters quoted the president as saying.

But he did not address Russia's claims that its military had cleared out Ukrainian forces from almost all of the besieged port city, except for those holding out inside the Azovstal factory - a massive iron and steel plant on the outskirts.

A spokesman for Russia's defence ministry said some 2,500 Ukrainian soldiers were inside the plant, their exit blocked by Russian troops, according to the state news agency Tass. The BBC has not independently confirmed these reports.

Image source, Getty Images

It's now early morning across Europe, and past 02:00 in Kyiv. Here's some of what happened in the conflict on Saturday:

In Bucha, Ukrainians get to work:

Since Russian forces left towns like Bucha, just north of the capital Kyiv, residents have taken on the gruelling task of rebuilding their homes and their lives.

The BBC's Anna Foster reported on one small, hardy group working to get their town back on its feet.

Explosions continue in Kyiv and Lviv:

Russia continued to batter Ukraine with fresh air strikes.

In Kyiv, one person was killed and several were wounded, said Mayor Vitali Klitschko, who warned residents not to return over fears of further attacks.

Explosions were also reported in the western city of Lviv, officials said, where air defences reportedly destroyed four Russian cruise missiles.

Johnson barred from Russia:

Moscow has barred UK Prime Minister Boris Johnson and several of his senior ministers from entering Russia over what it called their "hostile" attitude towards the war in Ukraine.

It's the latest in a series of sanctions by Russia against Western leaders, including US President Joe Biden and Canadian Prime Minister Justin Trudeau.

Read more on the latest from Ukraine

Image source, Reuters

Russia has offered to spare the lives of Ukrainian soldiers fighting in the key port city of Mariupol - but only if they lay down their arms on Sunday.

The Russian government said Ukrainian soldiers and “foreign mercenaries” still fighting in Mariupol, which Russia says it has nearly taken control of, could lay down their weapons between 06:00 and 13:00 Moscow time (03:00-10:00 GMT) and their safety would be guaranteed.

Those doing so would be treated in line with the Geneva convention on prisoners of war, it said.

The statement did not say what would happen to any soldiers who refused to stop fighting - and said the offer was being made on "purely humane principles".

Russia says the only remaining Ukrainian troops in the city are contained in a small area around the Azovstal steelworks area.

The statement said Russian forces would "continuously broadcast" details of the offer to the soldiers still at Azovstal every 30 minutes throughout the night.

It also encouraged the troops not to wait for permission to surrender from Kyiv, but to make the decision themselves.

Earlier, President Zelensky warned that "eliminating" the remaining fighters in Mariupol would put an end to talks with Russia.

A video has emerged on social media of a second British member of the Ukrainian armed forces captured in Mariupol by Russians.

The man, who gives his name as Shaun Pinner, is shown saying he was fighting in Mariupol but has been captured and is now in the territory of the breakaway Donetsk People's Republic, in eastern Ukraine.

Mr Pinner is one of two prisoners mentioned by the wife of Ukrainian opposition leader Viktor Medvedchuk, arrested last week by Ukrainian security agents while attempting to flee to Russia, as a possible swap for her husband.

As we reported in an earlier post, in a video address to Boris Johnson, Oksana Marchenko calls on the UK PM to arrange an exchange between Mr Medvedchuk and Mr Pinner, along with Aiden Aslin, another Briton taken prisoner in Mariupol last week.

Mr Aslin's capture has already been widely reported, and his family has expressed grave concerns about his welfare.

Speaking of Boris Johnson and his ban on entering Russia, he wasn't alone. There are 12 others on the Kremlin blacklist announced today. They are:

• Theresa May, Johnson's predecessor as British prime minister
• Foreign Secretary Liz Truss
• Defence Secretary Ben Wallace
• Justice Secretary (and deputy PM) Dominic Raab
• Home Secretary Priti Patel
• Chancellor Rishi Sunak
• Transport Secretary Grant Shapps
• Energy and Industrial Strategy Secretary Kwasi Kwarteng
• Culture Secretary Nadine Dorries
• Armed Forces Minister James Heappey
• Scotland's First Minister Nicola Sturgeon
• Attorney General for England and Wales and advocate general for Northern Ireland Suella Braverman

That leaves 20 other senior politicians who make up Boris Johnson's cabinet but have not been named, as well as the first ministers of Wales and Northern Ireland.

Image source, Reuters

UK Prime Minister Boris Johnson has had his latest phone call with President Volodymyr Zelensky.

A statement from 10 Downing Street says that part of their conversation had centred on the situation in Mariupol and that the British prime minister had taken the opportunity to salute Ukrainian resistance in the city.

"The Prime Minister updated President Zelensky on new sanctions from the UK that came into force last week, and said the UK would continue to provide the means for Ukraine to defend itself, including armoured vehicles in the coming days," it said.

Details of the phone conversation come on the day it was announced Johnson has been banned from entering Russia because of what the country deemed to be the UK's "hostile stance" on the war in Ukraine.

It also comes a week after Johnson and Zelensky spoke face-to-face rather than on the phone, as the British PM made a flying visit to Kyiv.

Image source, Reuters

A total of 1,449 people were evacuated from Ukrainian cities through humanitarian corridors on Saturday, Ukraine says - but a local leader says Russian shelling of one city stopped those figures from being higher.

Serhiy Haidai, governor of the eastern Luhansk region, said that Russia had violated a ceasefire agreement by opening fire in the centre of the city of Lysychansk.

That prompted local residents to seek safety in their basements and not attempt their planned journeys.

Evacuations went on from other towns and cities including 42 residents from Severodonetsk, 11km away and 11 people from Rubizhne 21km to the north.

Kyrylo Tymoshenko, deputy head of Ukraine's presidential administration, made the announcement of the total number of 1,149 evacuations from across the country - but this was a lower number than he has announced on several previous days.

Image source, Reuters

Kyiv mayor Vitali Klitschko has issued an uncompromising message to Ukrainians who have fled the city in recent weeks - now is not the time to think about returning to their homes.

Some residents have been making their way back home in recent days after two weeks of relative calm in the capital city, but Klitschko pointed out that there had been a mortar shell attack in the Darnytskyi district overnight.

And this came after Friday's Russian attack on a factory producing Neptune anti-ship cruise missiles, like the ones that hit the Russian warship Moskva.

Klitschko, the former world heavyweight boxing champion, said residents should be wary of further attacks and also the danger of landmines in northern parts of the city.

And he added on his official Telegram channel: "Those Kyivites who left earlier and are already going to return to the capital, I ask you to refrain from this and stay in safer places.”

Toby Luckhurst and Mariana Maglych in Lviv

Image source, Toby Luckhurst

Since the start of the war, volunteers have poured into Ukraine to help deliver aid and garner support for the war effort against the Russian invasion.

At a hotel in central Lviv I meet Hollywood actor Liev Schreiber - star of Spotlight (2015), which won an Academy Award for Best Picture.

He’s in the country with the NGO Blue Check Ukraine, , externalwhich works to give financial support to people in Ukraine.

He has already spent a week in a food kitchen in Poland, cooking up meals for refugees.

"Cut my finger pretty bad," he said, holding aloft his hand.

He says he decided to come after "about a month of depression sitting on the couch watching the news" about the war.

After talking to his children about what it means to live in a democracy and to have freedoms, he decided to put his money where his mouth is.

"It actually really helps to get off my ass and do something!"

Schreiber’s grandparents were Ukrainian, and he described the US as a nation of grandchildren. "Almost all of us are at some point grandchildren of immigrants", he said.

"I think we all need to step it up right now, and recognise that we are more related than we are not."

And his message to the Ukrainian people? "Slava Ukraini!" he says - Long Live Ukraine.

The Russian defence ministry has published images showing what it says is the crew of the cruiser Moskva - the first time any sailors from the ship have been seen since its sinking.

A large group of sailors is seen on parade in the Crimean port city of Sevastopol, where they are inspected by the Commander-in-chief of the Russian Navy, Admiral Nikolay Yevmenov.

The ministry quoted Adm Yevmenov as saying the officers and crew would "continue their service".

It announced late on Thursday that the Moskva, the flagship of the Black Sea fleet, had sunk on stormy seas after a fire caused by exploding ammunition. Ukraine said it had sunk the ship with two Neptune missiles.

The loss of the ship has been described as a huge blow to Russian morale.

Though Russia said at the time that the crew had been taken to Sevastopol, this is the first time any evidence of the survival of any sailors has been shown.

Russia has not reported any casualties from the fire or the sinking.

However, an unnamed US official quoted by Reuters said Washington believed there were casualties, and Ukraine claims the ship's captain, Anton Kuprin, was killed on board.

Image source, Max Delany/AFP

A dozen sanctioned Russians are linked to an estimated £800m worth of property in the UK, analysis by the BBC reveals.

Multi-million pound country manors in the south of England and luxury flats in London's most expensive areas are among the homes which have been snapped up by figures linked to Vladimir Putin.

Some of the individuals deny ownership of the mansions, which may mean they are beyond the reach of the sanctions.

To get to the bottom of who owns what, the BBC carried out a detailed trawl of leaked offshore documents, the Land Registry and court papers - as well as previous reporting.

Read more:

Sanctioned Russian oligarchs linked to £800m worth of UK property

Image source, EPA

Ukraine's President Volodymyr Zelensky has said eliminating Ukrainian fighters in the southern port city of Mariupol will put an end to talks with Russia.

Referring to a town outside Kyiv that has been devastated by heavy shelling, Mr Zelensky told the Ukrainska Pravda , externalnews website: "Mariupol could be like 10 Borodyankas.

"I want to say that the elimination of our military, our guys, will put an end to all negotiations."

• Borodyanka: 'There are a lot of people left under the rubble'

He said Ukraine would trade neither its territory nor its people, adding: "The more places like Borodyanka there are, the harder it will be".

Earlier, Ukraine insisted its troops were still holding out in the ruins of Mariupol, where Ukrainian forces have been pushed back to the Azovstal metal works near the port.

A Jack Russell has been been hard at work helping to remove explosive devices left behind by Russian troops.

Patron is currently working in the Chernihiv region, north of Kyiv, and has so far helped to remove hundreds of devices.

Image source, Reuters

The wife of captured Ukrainian pro-Russian opposition leader Viktor Medvedchuk has called on UK Prime Minister Boris Johnson to help arrange an exchange between her husband and British nationals in the Ukrainian military taken prisoner by Russia.

"Mr prime minister, you have a great influence on President Zelensky," Oksana Marchenko said in an address on YouTube.

"If you are not indifferent to the fate of your subjects, help their family and friends return [them], help me return Viktor."

We recently reported the concerns of Aiden Aslin's family after Russian media reported his capture in the city of Mariupol. Mr Aslin, a dual national born in Newark, Nottinghamshire, was one of the two men mentioned by Ms Marchenko.

Russian Foreign Ministry spokeswoman Maria Zakharova said in her telegram channel she hoped Mr Johnson "would not be slow to respond".

Mr Medvedchuk was captured by Ukrainian security agents on Tuesday while apparently trying to flee to Russia. He had been under house arrest on suspicion of treason but escaped when Russia invaded in late February.

As well as leading the Opposition Platform - For Life party, he is a wealthy businessman with close links to Russian President Vladimir Putin.

But the Kremlin has previously said it would not consider him for an exchange because he is a "foreign politician".

Toby Luckhurst
Reporting from Lviv

The Ukrainian authorities have said at least one person has died after the Russian attack on the capital Kyiv overnight.

Explosions were also heard in Lviv last night. But officials in the region say this was because of the successful defence of the area - anti-aircraft units managed to destroy “four cruise missiles” fired by Russian Su-35 planes, according to the head of the regional government Makysm Kozytskyi.

In an update filed on Telegram Kozytskyi added that the jets took off from Baranovichi airfield in Belarus.

There has been no comment from Russia about the attack.

Image source, .

Image source, Reuters

The Foreign Office has not yet responded directly to today’s banning of 13 UK politicians from Russia, but a government spokesperson issued a statement denouncing the Russian invasion.

“The UK and our international partners stand united in condemning the Russian government’s reprehensible actions in Ukraine and calling for the Kremlin to stop the war," the spokesperson said.

"We remain resolute in our support for Ukraine."

British Prime Minister Boris Johnson and Foreign Secretary Liz Truss were among those barred from entering Russia over what Moscow called their "hostile" stance on the Ukraine conflict. Russia said it would expand the list of banned individuals.

Officials say Western sanctions imposed on Russia since 24 February represent the most serious measures ever imposed on any major economy.

• Sanctioned Russian oligarchs linked to £800m worth of UK property

In a statement announcing its travel bans, external, Russia's foreign ministry accused London of an "unbridled information and political campaign aimed at isolating Russia internationally, creating conditions for containing our country and strangling the domestic economy".

UK sanctions include asset freezes on Russian President Vladimir Putin and Russian Foreign Minister Sergei Lavrov, asset freezes and travel bans on Russian oligarchs, and sanctions against more than 1,200 individuals and entities close to Mr Putin. Many of these sanctions include travel bans.

Image source, EPA

Ukrainian fighters who remain in Mariupol and refuse to surrender will be eliminated, the head of the Russian-backed Donetsk people's republic (DPR) has said.

Russian-allied soldiers are close to capturing the southern city of Mariupol, but Ukrainian forces are thought to be resisting the onslaught from the port area and the Azovstal factory - a massive iron and steel plant.

Videos have emerged of Ukrainian forces vowing not to surrender their positions.

This week Moscow said more than 1,000 Ukrainian marines had surrendered in Mariupol, but Ukraine denied the claim.

Talking to journalists in Mariupol, DPR head Denis Pushilin said: "Those members of the regular army, like the marines you have seen, who are prepared to surrender have surrendered.

"Whereas the nationalists, that is members of the nationalist battalions, it appears, have no intention of surrendering, that is why they are to be eliminated."

Footage of Mr Pushylin making the statement, standing next to Chechen politician Adam Delimkhanov and surrounded by troops, was broadcast on Russian news channel Rossiya 24.

Mariupol lies in territory claimed by the so-called DPR and is of strategic significance to the Russian army as it seeks to establish a land route between Crimea in the west and Donbas in the east.

Anna Foster
Reporting from Kyiv

Olya Nyikolaena pokes out her tongue. “We don’t sell Russian caviar, ugh! Ukrainian!” she exclaims proudly, waving her hand over the colourful tins that fill her stall.

The day the war began, Kyiv’s Besarabsky Market locked its doors. Three days ago it finally reopened. Much of it is still dark and empty, but a trickle of customers are browsing the jarred pickles, meat and fresh fruit.

“It’s been hard earning money with everything closed”, says Olya. “Most people haven’t returned yet. They’re afraid.”

As Russian threats to Kyiv renew, Svetlana Mikolyvna tells me she shelters in the basement when the air raid sirens sound.

“We still worry a lot. But really slowly life is coming back to a kind of normality. Small shops and cafes are starting to reopen, you can see the tiny changes.”

“I don’t know why the Russians hate us so much” Olya adds. “We are a hospitable nation, happy to have guests, but not the ones that bomb you at 4am.”

Tom Bateman
Reporting from Dnipro

Image source, Reuters

There are reports that Mariupol will be completely closed for entry and exit from Monday, potentially sealing the city and preventing further humanitarian evacuations.

An adviser to the city's mayor, Petro Andryushchenko, said on Telegram earlier today that Russian forces plan to bar people from leaving or entering Mariupol starting from 18 April.

I’ve spoken to Deputy Mayor Serhii Orlov who says such a closure has already been in place for the last four or five days.

Mr Orlov is no longer in Mariupol but suggested he has contact with those who are. He told me that Russia plans to extend the policy for a further week from Monday. He added he believes Russian forces plan to implement “more strict” rules within the city involving checkpoints to monitor and restrict movement between districts.

Image source, .

“They ask for internal passes, and [those] who do not have these passes will go to ‘filtration’,” he says, referring to camps reportedly used before people are deported to Russia.

The military siege and collapse in communications in Mariupol means it is not possible to verify the reports.

Despite the report of a closure already in place, an official from Ukraine’s central government in Kyiv says more than 360 people from Mariupol arrived in Zaporizhzhia on Friday. It’s not clear when they left the city. The hazardous journey can often take several days.

On Friday Moscow said it had been opening “humanitarian corridors” every day from Mariupol “towards Russia” and routes from Mariupol to the nearby city of Berdyansk and to Zaporizhzhia.

It has not commented on freedom of movement within the city.

Image source, .