Image source, Reuters

The US has promised to increase its military aid to Ukraine, Foreign Minister Dmytro Kuleba says after meeting Joe Biden in Poland.

"No other country provided Ukraine with more support than the United States. And this is crucial," he says.

"Ukrainian stamina and Western weapons - mostly American weapons - is the recipe for success on the battleground."

He has not provided any details about the extra military assistance but says: "Today we did receive additional promises from the United States on how our defence co-operation will evolve."

Image source, PA Media

The UK should be doing "much more" to help Ukrainian refugees, the mayor of London has said at a march in support of the country.

A large crowd has gathered near central London's Hyde Park this afternoon for a march and vigil to send a unified message of support to the people of Ukraine.

Image source, PA Media

"Londoners over the last few weeks have shown that we're opening our arms to Ukrainian refugees, whether it's by donating money to those charities doing a brilliant job in Ukraine or by opening our homes to those fleeing Ukraine," Khan says.

He says it's important over the next few weeks to make it much "easier for those who are fleeing Ukraine to come here", suggesting other European nations have performed better.

Image source, PA Media

Protesters draped in the Ukrainian colours of yellow and blue have been making their way towards Trafalgar Square.

Chants of "we stand with Ukraine" ring out as traffic is brought to a standstill.

Image source, Reuters

Image source, Reuters

If you're just joining our live coverage, welcome. Here are some of the main developments you may have missed:

• Three powerful explosions have been heard in Lviv and thick black smoke has been seen rising over the outskirts of the city in the west of Ukraine
• US President Joe Biden has held talks with Ukraine's defence and foreign ministers in Poland - the highest level face-to-face meetings since the war began
• Ukraine's defence minister says Biden promised extra military aid, but did not give any details
• Biden says Putin expected to divide Nato and was surprised this didn't happen
• Yet another Russian general has been killed in Ukraine. Lt Gen Yakov Rezantsev is the seventh to die since the war began, according to Western defence officials

• Russian forces have taken control of Slavutych, the city where workers of the defunct Chernobyl nuclear power plant live, but local residents have staged protests, waving Ukrainian flags and singing patriotic songs
• Russian TV stations have broadcast a video of Defence Minister Sergei Shoigu holding talks with senior generals. He had not been seen for two weeks and there had been speculation about the state of his health.

We're getting reports of several explosions in the western Ukrainian city of Lviv. This picture shows plumes of black smoke rising in the distance.

We'll bring more details as they emerge.

Image source, Reuters

We reported earlier that Kyiv's mayor Vitali Klitschko had announced a curfew in Ukraine's capital from this evening until Monday morning but this has now been cancelled.

He has not given any reason for the change except that he has received "new information from the military command".

The usual night-time curfew from 20:00 (18:00 GMT) to 07:00 will remain in force but people will "be able to freely move around Kyiv on Sunday during the day", he says on Telegram.

Image source, .

More now from Slavutych, the city where workers of the now-defunct Chernobyl nuclear power plant live.

Earlier it was reported that Russian forces had taken control of the city and that the mayor had been taken hostage.

Their actions brought thousands of angry protesters onto the streets, waving Ukrainian flags and chanting patriotic slogans.

A Slavutych resident who took part in the protest told the BBC that the "invaders" had now moved back to the entrance of the city, and the Ukrainian flag still flies above the local administration building.

The resident said the city's mayor spoke at the rally after the reports of his kidnapping, suggesting he had been released again.

Slavutych was built after the 1986 disaster at the Chernobyl nuclear power station, when a reactor exploded releasing radioactive material into the environment.

The site of the power plant itself has been under the control of Russian forces since the first day of the war.

Around 300 workers were trapped there after it was seized, although some have now been able to leave.

Image source, Reuters

US President Joe Biden says he thinks Russian leader Vladimir Putin has been surprised to find he hasn't been able divide Nato allies in their reaction to his invasion of Ukraine.

Biden has been speaking during a trip to the Polish capital Warsaw, which has seen him meet Ukrainian government ministers, as well as Poland's President Andrzej Duda.

"I'm confident that Vladimir Putin was counting on being able to divide Nato, being able to separate the eastern flank from the west, being able to separate nations based on past histories," Biden said.

"But he hasn't been able to do it - we've all stayed together.

"I just think it's so important that we, Poland and the United States, keep in lock step how we're proceeding."

He also says history has shown the importance of the US not remaining on the sidelines during conflict in Europe.

"We have learned from sad experience in two world wars, when we've stayed out and not been involved in stability in Europe, it always comes back to haunt us in the United States.

"So I've been saying for a long time, as senator who visited here and a member of the Foreign Relations Committee, as vice president and now as president, that stability in Europe is critically important to the United States in terms of our interest - not only in Europe but around the world."

Image source, PA Media

Two private jets owned by a sanctioned Russian oligarch have been seized by the British government.

The jets belonging to billionaire oil tycoon Eugene Shvidler had been under investigation at Farnborough and Biggin Hill airports for three weeks.

Transport Secretary Grant Shapps said "Putin's friends" should not "enjoy luxuries" while innocent people die in Ukraine.

Shvidler was sanctioned over his business ties with Chelsea FC owner Roman Abramovich.

His net worth has been estimated at £1.2bn, the government says, while the seized jets are believed to be worth up to $60m (£45m).

BBC Monitoring
The world through its media

Ukrainian FM radio stations are no longer available in the southern city of Kherson occupied by Russian troops, the Ukrayinska Pravda news website has tweeted, external.

It quotes local residents as saying only Russian radio stations are on the air.

Ukraine's General Staff of the Armed Forces said in its regular morning update earlier that Kherson was one of the areas where Russia had deployed more military units in order to "suppress the resistance of the residents".

Image source, Denis Nasik/Wikimediacommons

Another Russian general, Lt Gen Yakov Rezantsev, has been killed in a strike near the southern city of Kherson, Ukraine's defence ministry says.

Rezantsev was the commander of Russia's 49th combined army.

A Western official says he's the seventh general to die in Ukraine, and the second lieutenant general - the highest rank officer reported to have been killed.

It's thought low morale among Russian troops has forced senior officers closer to the front line.

Ukrainian media reports the general was killed at the Chornobaivka airbase, which Russia is using as a command post and has been attacked by Ukraine's military several times.

Image source, EPA

Russian forces have taken control of Slavutych, the town housing workers for the defunct nuclear power plant of Chernobyl, according to the regional governor, Oleksandr Pavlyuk.

He posted a message on the Telegram messaging app saying Russian soldiers had seized the town's hospital and kidnapped the mayor.

Slavutych was built for the evacuated personnel of the Chernobyl plant after the 1986 disaster - the world's worst ever nuclear accident.

On Friday, the UN's nuclear watchdog warned that fighting in the town was stopping workers from travelling to and from the plant, which still houses several nuclear waste containment facilities.

Russian forces seized Chernobyl itself right at the start of the conflict.

Image source, evn

After two weeks of fevered speculation about the disappearance of Russian Defence Minister Sergei Shoigu, his ministry has released a clip of him addressing a meeting of senior generals.

Reading from a script, and occasionally slurring his lines, Shoigu talked about the supply of weapons to troops in Ukraine.

There's been intense speculation that he is having health problems, or has had a heart attack.

There was nothing to indicate when the footage was filmed.

Image source, Reuters

US President Joe Biden is holding talks with two Ukrainian ministers in Poland - his first face-to-face meeting with such high-level officials since Russian forces invaded the country a month ago.

The White House said he would "drop by" a meeting between US Secretary of State Antony Blinken and US Defense Secretary Lloyd Austin with their Ukrainian counterparts, Dmytro Kuleba and Oleksii Reznikov.

Biden has been in Poland since Friday and is also meeting his Polish counterpart, Andrzej Duda. He is set to deliver a major speech about the conflict later on Saturday.

Some say the fact that the Ukrainian ministers are leaving their country is a sign of their growing confidence in how the war with Russia is going.

We've just learned that the mayor of Kyiv is extending the curfew in the Ukrainian capital from 20:00 local time (18:00 GMT) on Saturday until 08:00 on Monday.

Mayor Vitali Klitschko said in an online post that the decision was made by the Ukrainian military, without giving further details.

The mayor of Mariupol said he had discussed how to evacuate civilians from the besieged Ukrainian port city with the French ambassador to the country, according to the Reuters news agency.

French President Emmanuel Macron says he will hold talks with Russia's Vladimir Putin about how to help the 100,000 people still trapped in the city.

The evacuation plans also involve Greece and Turkey.

Mariupol mayor Vadym Boichenko also told national television that street fighting was taking place in the city centre.

Russia's initial strategy in Ukraine has failed and its army now has to decide what to do next, a top military analyst has told the BBC.

Phillips O'Brien, who is professor of strategic studies at the University of St Andrews, said many foreign observers had taken the "easy intellectual way out" of assuming that Russian military superiority would prevail in the war.

However, this was "a very false opinion" of Russia's capabilities that did not take into account whether its soldiers were willing to take risks, he said.

At the same time, Ukraine's capabilities had been underestimated, he added.

Ukrainians had been preparing for war since Russia's annexation of Crimea in 2014 and did not want to live "under a Russian dictatorship", Prof O'Brien said.

"Now Russia has to decide what to do: they can either escalate up or they can escalate down," he added.

Escalating down would be the most rational course of action and would involve trying to reach a deal, but "they don't seem to be willing to do that now", he said.

Escalating up would mean either rebuilding the army from scratch or "opening up a can of worms" by resorting to chemical, biological or nuclear weapons.

"Either they escalate down or escalate up, but what they have now can't do the job," he concluded.

Adam Easton
Warsaw Correspondent

Image source, Reuters

The number of people fleeing Ukraine for Poland has started to fall in recent days, with 30,500 crossing on Friday, down 6.4% from the previous day, the Polish Border Guard said on Saturday.

By 0600GMT on Saturday, 6,100 people had crossed - that’s down 11% from the same period on Friday.

More than 2.2 million people have crossed in to Poland since the war began, the agency wrote on Twitter.

Some of those people fleeing Ukraine have already left Poland, but Warsaw University migration expert Prof Maciej Duszczyk estimates around 1.2-1.3 million refugees remain.

More than 300,000 people have entered Ukraine via Poland since the war began, the agency said.

Jeremy Bowen
BBC News, Irpin

Image source, Jeremy Bowen

Shane Matthews, a former British soldier who travelled here from the UK with a Ukrainian friend, was part of Commander Oleg's unit in Irpin - just to the north-west of Kyiv.

A medic and sniper, Shane said he had seen many dead civilians there, including a family of four whose car was hit by an artillery shell. So little was left of them, he said, that their remains would barely have filled a bin bag.

Unlike every Ukrainian from the president down, Shane did not believe Nato should intervene in Ukraine because of the risks of a wider war.

Read more - Next stop Kyiv: the battle on the capital's outskirts

In its latest update, the UK ministry of defence says it is likely Russia will continue to use its heavy firepower on urban areas as it looks to limit its own already considerable losses, at the cost of further civilian casualties.

Forces seemed to be proving reluctant to engage in large-scale urban infantry operations, rather preferring to rely on the indiscriminate use of air and artillery bombardments in an attempt to demoralise defending forces, the update said.

The statement added that Russian forces continue to besiege a number of major Ukrainian cities including Kharkiv, Chernihiv and Mariupol.

The war in Ukraine has killed 136 children so far, Ukraine's office of the prosecutor general said on Saturday in a message on the Telegram messaging app.

It added that the number of wounded children stood at 199.

The BBC has not been able to verify this information.