A senior US defence official said Moscow's offensive was going much slower than planned, with the Kremlin seeking to capture Ukraine's industrial Donbas region.

The US has accused the Russian president of acting with "depravity" in his attack on Ukraine.

Angelina Jolie makes surprise visit to Lviv - Ukraine latest

Ukrainian President Volodymyr Zelenskyy said Russia was attempting to "empty" the Donbas of people and peace talks were in danger of collapsing.

Key developments:
• The Foreign Office is investigating reports that a British national has been detained by Russia after a video emerged showing a man in camouflage clothes being questioned
• The family of a former US Marine say he was killed while fighting alongside Ukrainian forces, in what would be the war's first known death of an American in combat
• Hollywood star Angelina Jolie, a special envoy to the UN, is reportedly seen in the Ukrainian city of Lviv
• Emmanuel Macron tells Mr Zelenskyy that France will strengthen its military and humanitarian support for Ukraine
• Russian foreign minister Sergei Lavrov says Russian and Ukrainian negotiators talk "almost every day" but "progress has not been easy"
• Russian forces have stolen "several hundred thousand tonnes" of grain in the areas of Ukraine they occupy, a Ukrainian minister says

The UK's Ministry of Defence (MoD) said Russia was facing "considerable challenges" and it had been forced to merge and redeploy "depleted and disparate units from the failed advances in northeast Ukraine".

"Many of these units are likely suffering from weakened morale," the MoD said.

"A lack of unit-level skills and inconsistent air support have left Russia unable to fully leverage its combat mass, despite localised improvements."

Russian troops turned their focus towards Ukraine's east and south as they moved into the second phase of their invasion after failing to capture the capital city of Kyiv.

Russia trying to 'empty' Donbas of people, says Zelenskyy

Mr Zelenskyy accused Moscow of carrying out "constant brutal bombardments" on buildings and residential areas of the eastern region of his country.

He compared the barrage of attacks as similar to the situation in Mariupol - a key port city that has been largely destroyed after being hit by almost daily strikes since the Russian invasion began in February.

Mr Zelenskyy said: "If the Russian invaders are able to realise their plans even partially, then they have enough artillery and aircraft to turn the entire Donbas into stones. As they did with Mariupol."

He added that the southeastern city has been turned into a "Russian concentration camp among the ruins".

Inside Mariupol, a battle has been taking place at the Azovstal steel plant, which has become the last stronghold in the area.

Ukrainian troops have successfully fought off Russian forces so far, but the mayor of Mariupol, Vadym Boichenko, said the situation is dire and citizens are "begging to get saved".

"It's not a matter of days, it's a matter of hours," he said.

US accuses Russia of 'depravity in innocent people'

Pentagon spokesman John Kirby described Russia's invasion of Ukraine as "brutality of the coldest sort" and said it was "hard to look at" what Mr Putin was doing to the country.

He said: "I don't think we fully appreciated the degree to which he would visit that kind of violence and cruelty and as I said depravity, on innocent people, on non-combatants, on civilians, with such utter disregard for the lives he was taking."

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Mr Kirby appeared to get emotional as he spoke of the scenes emerging from Ukraine, saying: "It's difficult to look at some of the images and imagine that any well-thinking, serious mature leader would do that. I can't talk to his psychology, but I think we can all speak to his depravity."

He also said it was "not entirely clear how truthful the information was" that the Russian leader was getting but there were "indications that he wasn't necessarily getting an accurate picture".