The White House said the US has evidence that the war against Ukraine has been “a strategic disaster” for Russia. “We have seen incontrovertible evidence that this has been a strategic disaster for Russia,” director of communications Kate Bedingfield said, adding that Russia is “working to redefine the initial aims of their invasion”.

US president Joe Biden said that Russian president Vladimir Putin “seems to be self-isolated” and noted “there’s some indication that he has fired or put under house arrest some of his advisers,” without citing evidence.

UK defence secretary Ben Wallace said Putin was “not the force he used to be” and a “man in a cage he built himself”. Wallace told Sky News: “He is isolated. His army is exhausted, he has suffered significant losses. He has not only got to live with the consequences of what he is doing to Ukraine, but he has also got to live with the consequences of what he has done to his own army.”

Russia has threatened to halt contracts supplying Europe with a third of its gas unless they are paid in Russian currency. Putin signed a decree on Thursday saying foreign buyers must pay in roubles for Russian gas from Friday. He said contracts would be halted if these payments were not made. Germany and France rejected the demands and said they amounted to “blackmail”.

Ukrainian president Volodymyr Zelenskiy repeated his warning that Russia is preparing for “powerful strikes” in the Donbas region after appearing to withdraw from an assault on Kyiv. The Pentagon also said that Russia may be repositioning some of its forces to send them to the Donbas.

Nato’s chief Jens Stoltenberg said Russian forces are not withdrawing, but regrouping. He also said the alliance had yet to be convinced Russia was negotiating in good faith in peace talks in Istanbul because Moscow’s military objective since launching its invasion of Ukraine had not changed.

Peace talks between Russia and Ukraine were due to restart online on Friday morning.

Russia is redeploying elements of its forces from Georgia to reinforce its invasion, British military intelligence said on Thursday. “It is highly unlikely that Russia planned to generate reinforcements in this manner and it is indicative of the unexpected losses it has sustained during the invasion,” the ministry added.

A humanitarian corridor is set to be opened from 10am on Friday morning to allow civilians out of the besieged port city of Mariupol, which is in the Donbas in south-eastern Ukraine. It follows “a personal request from the French president and German chancellor to Russian president Vladimir Putin”, it said.

A convoy of Ukrainian buses has set out for Mariupol to try to deliver humanitarian supplies and bring out trapped civilians, Ukraine’s deputy prime minister said.

EU and Chinese leaders will meet for a first summit in two years on Friday, with Brussels keen for assurances from Beijing that it will neither supply Russia with arms nor help Moscow circumvent western sanctions. EU officials close to the preparations of the summit said any help given to Russia would damage China’s international reputation and jeopardise relations with its biggest trade partners – Europe and the United States.

Russian forces have reportedly left the Chernobyl power plant, the Ukrainian Atomic Energy Ministry said, citing personnel at the site. Russian troops began leaving after soldiers got “significant doses” of radiation from digging trenches at the highly contaminated site, Ukraine’s state power company said. Energoatom said the Russians had dug in the forest inside the exclusion zone around the now-closed plant and “panicked at the first sign of illness,” which “showed up very quickly”. Energoatom later said Russian forces had taken Ukrainian soldiers as hostages when they left.

Britain and its allies have agreed to send more lethal military aid to Ukraine to help defend it against Russia’s invasion, the British defence secretary, Ben Wallace, has said. As part of the agreement, armoured vehicles and long-range artillery will be sent.

Australian prime minister Scott Morrison has said Australia will send armoured four-wheel-drive Bushmaster vehicles to Ukraine after Zelenskiy specifically asked for them during a video appeal to Australian lawmakers on Thursday. Morrison said the vehicles would be flown to Ukraine but didn’t specify how many would be sent or when.

France’s military intelligence chief Gen Eric Vidaud is leaving his post after Paris failed to accurately predict – in contrast with western allies – that Russia would launch a full-scale invasion of Ukraine, several sources with knowledge of his exit have said.

The Biden administration has approved the drawdown and sale of 30m barrels of petroleum from from the Strategic Petroleum Reserve (SPR) citing a severe energy supply interruption due to the war.