Russian forces have now “fully withdrawn” from northern Ukraine into Belarus and Russia, the UK Ministry of Defence (MoD) has said.

“At least some of these forces will be transferred to East Ukraine to fight in the Donbas,” it added in its intelligence update, posted on Twitter just after 6am.

The MoD continued: “Many of these forces will require significant replenishment before being ready to deploy further east, with any mass redeployment from the north likely to take at least a week minimum.

“Russian shelling of cities in the east and south continues and Russian forces have advanced further south from the strategically important city of Izium which remains under their control.”

The mayor of Bucha, near Kyiv, said investigators have found at least three sites of mass shootings of civilians during the Russian occupation.

Most victims died from gunshots, not from shelling, he said, and some corpses with their hands tied were “dumped like firewood” into recently discovered mass graves, including one at a children’s camp.

Mayor Anatoliy Fedoruk said the count of dead civilians stood at 320 as of Wednesday, but he expected the number to rise as more bodies are found in his city, which once had a population of 50,000. Only 3,700 now remain, he said.

In his nightly address on Thursday, Ukrainian President Volodymyr Zelensky suggested that the horrors of Bucha could be only the beginning.

In the northern city of Borodianka, just 18 miles northwest of Bucha, Mr Zelensky warned of even more casualties, saying “there it is much more horrible”.

Moscow has denied targeting civilians and says images of bodies in Bucha were staged by the Ukrainian government to justify more sanctions against Moscow and derail peace negotiations.

Dmitry Peskov, press secretary to Russian president Mr Putin, confirmed Russia had sustained “significant losses of troops” in the war, calling the deaths a “huge tragedy”.

Speaking to Sky News, Mr Peskov denied Russian forces were behind the deaths of Ukrainian civilians in places such as Bucha, which is situated on the outskirts of the capital, instead calling the photos a “bold fake”.