US President Joe Biden has accused "dictator" Vladimir Putin of genocide.

Speaking in Iowa about domestic energy costs, Biden went further than any other member of his administration in describing civilian killings in Ukraine.

US officials have accused Russia of committing war crimes, but have not until now gone so far as to call it "genocide".

Biden later said it would be up to lawyers to decide if genocide had been committed.

"It sure seems like genocide to me," he told reporters after his speech.

Image source, Getty Images

Prominent Putin opponent Vladimir Kara-Murza has been jailed for 15 days in Russia for "disobeying police orders".

His lawyer, Vadim Prokhorov, published a police report on his client's arrest, which said he had behaved strangely and resisted arrest.

It was not explained in court why police were waiting for Kara-Murza, the lawyer said.

A former associate of murdered opposition leader Boris Nemtsov, Kara-Murza is a vocal critic of the war, and co-founder of a group that has called for Russia's political and military leaders to be declared war criminals.

He claims he has twice been poisoned by the authorities, in 2015 and 2017.

Image source, Getty Images

Speaking at an event in Iowa about the costs of domestic energy, US President Joe Biden has described Russia's actions in Ukraine as "genocide".

The phrase marks a first for the White House administration, which has so far avoided the highly-charged term to describe Russia's killing of civilians.

"Your family budget, your ability to fill up your tank - none of it should hinge on whether a dictator declares war and commits genocide a half a world away," Biden said.

Ukraine's President Zelensky has described the killings of civilians in the town of Bucha near Kyiv – which has sparked widespread accusations of war crimes – as "real genocide".

And earlier on Tuesday, Ukraine's president said that new mass graves are being uncovered "almost daily" in regions that had been previously occupied by Russia.

Ready more: Do Bucha civilian killings amount to genocide?

Toby Luckhurst
Reporting from Lviv

As night falls in western Ukraine a convoy of British vehicles pulls into a car park in the suburbs of Lviv.

Simon Waller, a former soldier in the Royal Corps of Signals, has driven one of 16 cars from Birmingham across the continent to Ukraine for the humanitarian group Dobrovoz.

The 55-year-old says he was inspired to help because of friends he has in Kharkiv, who he met seven years ago on a scuba diving trip in the Maldives. After the invasion he was "in shock" for weeks, until they told him the country needed drivers.

"I said, I'm in, I'll quit my job, I want to do something to help you, help your friends, help your family, help Ukraine," he says.

Simon put the word out online among former army friends, and soon he was part of a convoy of vehicles heading to the war.

"The last trip out here, the vehicle I drove out… the next morning we had a photo of it on the frontline in Kyiv," he said. "That was just the best feeling. It was being used literally within 12 hours."

Asked how best people in the UK can help, he says there's "an awful lot people can do" – but to be mindful of how best to do it.

"Don't just donate clothes. Some people do need the clothes but it's better [Ukrainians] can buy clothes for themselves, in one way or the other," he says.

"Everybody wants to help but they don't often think about how they’re helping."

Image source, Getty Images

Ukrainian First Lady Olena Zelenska says that she and President Volodymyr Zelensky have been living separately for more than a month to protect her and her children.

She told CNN via email, external: "Volodymyr and his team actually live in the president's office. Due to the danger, my children and I were forbidden to stay there. So, for more than a month we communicate only by phone."

Zelenska said her husband has "shown the same traits" that he exhibits as a "wonderful father" in his wartime leadership.

"He has not changed. It's just that more people saw it through my eyes," she said.

Zelensky's wife said she feels like she is "walking a tightrope" and will "lose time and balance" if she thinks about how she is doing it.

The first lady said that the war must not become "habitual" and Ukraine's dead must not become statistics.

"Don't get used to our grief!" she said.

Image source, Getty Images

Secretary of State Anthony Blinken says the US is not in a position to confirm reports that Russian forces have used chemical weapons in the besieged southern port city Mariupol.

However, Blinken says the US has "credible information" that Russia "may use... chemical agents" in the besieged port city.

"We share that information with Ukraine... and we're in direct conversation with partners to try to determine what actually is happening, so this is a real concern," Blinken says.

The Organisation for the Prohibition of Chemical Weapons (OPCW) has also said it is concerned by the unconfirmed report of chemical weapons use and that it is monitoring the situation closely.

Verifying claims by Ukraine's Azov regiment that three soldiers were injured by "a poisonous substance" in an attack yesterday is very difficult, as Mariupol is still surrounded by Russian forces.

Image source, EPA

The mayor of the besieged port city of Mariupol says an estimated 21,000 people have died there but that officials have had to stop counting bodies due to street fighting, Reuters reports.

Mayor Vadym Boychenko also said that bodies were disappearing from the streets and that he suspected Russian forces were responsible.

The BBC has been unable to independently verify this claim.

Image source, .

Aleem Maqbool
Religion editor, BBC News

Image source, BBC News

"I'm Archbishop Rowan Williams from England, I come with greetings and love and prayers from my brothers and sisters in England for all of you brothers and sisters here."

The displaced families that Dr Williams is addressing in a large room in a converted health centre in Chernivtsi in western Ukraine, break into applause.

To the side of the former Archbishop of Canterbury stands a rabbi, a Hindu spiritual leader and a Buddhist nun.

Together with monks, a Bosnian Mufti, a Greek Orthodox Archbishop and other Jewish faith leaders they made for a remarkable delegation, brought together in a country under siege by a mission to try to provide some degree of comfort.

But all of them acknowledged their words were unlikely to have any real bearing on the horrors still unfolding to the east. There are questions as to whether something more tangible can be done, for example, to put pressure on a Russian Orthodox Church leadership that has given its blessing to the war.

Ukraine's security service says it's arrested fugitive pro-Russian politician Viktor Medvedchuk, who had been under house arrest on suspicion of treason but went on the run days after the Russian invasion.

Medvedchuk, who says Putin is godfather to his daughter, denies wrongdoing. A photograph on social media appears to show him looking dishevelled, in handcuffs and wearing military fatigues.

The Kremlin spokesman says he has seen the image but cannot say whether it is genuine.

Image source, Getty Images

Prime Minister Boris Johnson and US President Joe Biden have spoken on the phone about the need to ratchet up economic pressure on Russia and end Western reliance on the country's oil and gas.

"The leaders discussed the need to accelerate assistance to Ukraine, including bolstering military and economic support, as the Ukrainian forces prepare for another Russian onslaught in the east of the country," a Downing Street spokeswoman said.

Steve Rosenberg
BBC Russia editor

Image source, .

In Stavropol cemetery, there is a new line of graves.

The fresh mounds of earth are covered in a sea of flowers. Decorating the graves, fluttering in the breeze, are military banners with emblems of elite Russian units.

Fixed to wooden crosses are the portraits of soldiers, their names and the dates they died.

The servicemen buried here lost their lives after 24 February: the start of President Putin's "special military operation" in Ukraine.

At the cemetery I meet Dmitry. He lays red carnations at the grave of his former paratrooper comrade, an officer called Sergei Tysyachny.

"I don't believe these fakes," Dmitry says about war crime allegations levelled against some Russian soldiers. "I will never believe them.

"I know how my commander, Sergei, taught us to act. I trust my comrades and my army. They would never do things like this."

You can read Steve Rosenberg's full report here.

Ukrainian President Volodymyr Zelensky, speaking to the Lithuanian parliament earlier today, said there are "thousands and thousands of victims" and "hundreds of cases of brutal torture" being discovered in areas reclaimed from Russian forces by Ukraine.

"New mass graves are found almost daily. Bodies continue to be found in drains and cellars," he said.

Officials in Ukraine's capital Kyiv will continue to "investigate war crimes" carried out by the Russian military, Zelensky told Lithuanian MPs.

Image source, Reuters/Marko Djurica

He's sure Russia will deny the allegations but the crimes will be "on the conscience of the Russian propagandists".

Ukrainian prosecutors have said today that six people have been found shot dead in a Kyiv building basement.

Russia has repeatedly denied accusations of war crime and has blamed Ukraine.

Image source, EPA

Officials in Bucha say they've now found 403 bodies of civilians who they believe were killed during an occupation by Russian troops.

The city's mayor Anatoliy Fedoruk says the toll is still growing, as other residents remain missing.

Images of dead bodies in the streets have prompted global outrage, and allegations of war crimes have been levelled at the Kremlin.

Russia has again denied its troops were to blame - with President Putin today claiming images of civilian bodies were faked.

James Landale
Diplomatic correspondent

Image source, Crown Copyright 2016

The head of the UK’s army has predicted the war in Ukraine could end in what he called “a military, tactical stalemate”.

General Sir Mark Carleton-Smith also suggested the conflict should prompt a rethink of the government’s decision to cut the size of the British army.

The chief of the General Staff told the Policy Exchange think-tank that Russian forces were at “an operational pause” as they regrouped ahead of an expected offensive in eastern Ukraine.

“Whether that proves to be the decisive battle or not, we are currently measuring this campaign in days. We ought to expect to measure it in months, if not – in the scheme of things – in years,” he said.

“The most likely immediate and interim outcome is a military, tactical stalemate in the Donbas, with a Russian regime able to claim some measure of success, and that potentially acting as a potential launch point for a subsequent campaign.

"I don’t think the international community and Europe, of course, is going to be able to live comfortably with a frozen conflict in Europe.”

Image source, Getty Images

More now on claims that Russian forces used chemical weapons in the besieged port city of Mariupol.

There has so far been no evidence proving that such weapons have been used. But how would we know if they had been?

The global watchdog for chemical weapons - the Organisation for the Prohibition of Chemical Weapons - would usually be called in to assess any evidence. But that will be challenging in Mariupol, which is surrounded and struggling to get even basic supplies.

The former British Army officer Hamish de Bretton-Gordon, a chemical weapons expert, cautioned that even if uncontaminated samples could be collected from the scene they would need to be taken to another country for analysis.

This, he said, would take some time.

You can read more here on how chemical weapons use is detected, and what might happen if Russia did use them.

Gordon Corera
Security correspondent, BBC News

Ukrainian authorities say they foiled an attempt to disrupt their energy infrastructure through a cyber-attack.

They say the hackers first got inside systems by February. They then tried to activate the malicious software they had implanted on 8 April. This could have switched off power supplies.

This type of attack has been carried out in Ukraine before as far back as 2015. However, authorities say this time the attack was foiled.

Those responsible are said to be a hacking group known as Sandworm, linked to Russian military intelligence and a series of previous operations (always denied by Moscow).

“Sandworm is an apex predator, capable of serious operations, but they aren’t infallible,” says John Hultquist from the cyber-security company Mandiant.

They may have been seeking to carry out the attack in support of military operations in the region that was targeted.

Ukraine has been subject to a series of cyber-attacks in the run up to and since the invasion began but has surprised many observers by defending itself against them better than expected.

Adam Durbin
BBC News

Image source, Getty Images

The control of a steel factory has become a focal point in the battle for control of Mariupol, with fierce fighting and even reports of hand-to-hand combat in the warrens of the massive industrial complex used by Ukrainian defenders.

The Azovstal iron and steel works is one of the key operating bases left for the several thousand Ukrainian fighters remaining in the besieged city - but exact numbers using it are unclear because of a lack of reliable information, experts say.

Rumours it had been attacked by chemical weapons have been circulating, but the BBC has not been able to verify these allegations.

Dr Aglaya Snetkov, an expert in Russian foreign and security policy from University College London, explains the factory has been a key objective through the weeks-long siege of the Black Sea port city.

However, she explains the reason the Soviet-era facility has so far resisted capture is that it was built to withstand significant damage, and it is so large that it has proven difficult to flush out fighters - which include elements from the far-right, nationalist Azov battalion - based there.

Snetkov says the plant, as well as Mariupol more broadly, has demonstrated the challenges of urban warfare and capturing areas with a "lot of fighters that keep going and can essentially have hideouts".

Image source, .

The heavily defended area is one of Mariupol's last remaining pockets of resistance, intelligence expert Justin Crump explains.

Describing the nature of the fighting, the former British Army officer describes it as complex battles in amongst dense industrial buildings.

Crump says the focus of the Russian assault has primarily been bombing the area as part of a painstaking and slow tactic of "wearing down the defenders" occupying the vast site.

He explains this means they have been using heavy artillery to destroy buildings which could be used by defenders, advancing afterwards to reduce the deaths of their own soldiers.

Crump adds the Ukrainian troops are in surprisingly "good order" given the brutal bombardment for many weeks, but are in an increasingly difficult situation after their supplies of ammunition and food have been cut off for over a week. Many are increasingly being forced to surrender, he says.

As we've been reporting, Vladimir Putin has said peace talks between Ukraine and Russia have stalled.

Here's the latest from the Russian president - and the view from the Ukrainian side:

• Putin says talks with Ukraine "have again returned to a dead-end situation for us" while meeting his Belarusian ally Alexander Lukashenko
• He also says Russia's "military operation" will continue, blaming Ukraine for "inconsistency in key issues" from talks and "fake claims" about war crimes

• However, Ukrainian presidential adviser Mykhailo Podolyak has today told Reuters that although negotiations are "extremely difficult", they will continue
• Podolyak said he believes Russia is trying to put pressure on future peace talks by making public statements beforehand

Image source, UKRAINIAN PRESIDENTIAL PRESS SERVICE/REUTERS

When were the last in-person talks?

• Peace talks were held in person on neutral ground in Turkey's capital Istanbul at the end of March
• Russia agreed to "drastically reduce" military combat operations around the capital, Kyiv, and the northern city of Chernihiv "to boost mutual trust"
• However, Putin today accused Ukraine of "inconsistency in key issues" and "moving away from its agreement in Instanbul," Interfax news agency reports
• Ukraine's President Volodymyr Zelensky has said peace talks will continue virtually with Russia, despite accusing Moscow of war crimes and genocide

Image source, REUTERS/KEMAL ASLAN

More now on claims we reported earlier of chemical weapons being used in the beseiged port city of Mariupol.

A senior US defence official has said the country cannot confirm the use of chemical agents, Reuters reports.

The official, who spoke to reporters on the condition of anonymity, said the US has no information to support the movement of chemical agents in or near Ukraine.

The US and Britain have both been looking into the reports after Ukraine's Azov regiment said three soldiers were injured by "a poisonous substance" in an attack yesterday.

However, no evidence has been presented to confirm the use of chemical weapons.

Ascertaining what is happening in Mariupol is currently very difficult as it is surrounded by Russian forces and supplies of food and medical supplies are running low.

Jonathan Beale
Reporting from Donbas

People in eastern Ukraine know the Russians are about to step up their offensive here. Even the dogs on the streets seem to know, and can be heard barking whenever there's a heavy thump of artillery in the distance.

Hundreds of thousands of people have already fled to the relative safety of western Ukraine. Once again large columns of Russian vehicles have been spotted by satellite - this time heading towards the east.

Here in Donbas we've also seen signs of Ukraine bringing in more military equipment, including armoured vehicles and longer range air defence systems. But not in the volume of Russia's reinforcements.

Ukraine may be being more tactically astute about their movements, or simply have less. Both are probably true.

Many believe this next phase of the war in the east could decide the outcome of this conflict. Many also expect it to be bloody.

Read Jonathan Beale's full report here