Moscow releases 215 prisoners in exchange for former Ukrainian MP Viktor Medvedchuk and others

• Russia-Ukraine war – latest updates

More than 200 Ukrainian and foreign citizens have been released from Russian captivity, including fighters who led the defence of the Azovstal steelworks in Mariupol, in the biggest prisoner swap since Russia’s invasion of Ukraine in February.

In return, Russia received 55 prisoners from Ukraine, including the former Ukrainian MP Viktor Medvedchuk, an ally of Vladimir Putin accused by Ukraine of high treason.

Putin threatens use of nuclear weapons as he announces partial mobilisation in Russia; World leaders condemn intention by Moscow-held regions of Ukraine to vote on annexation by Russia

Vladimir Putin has given a national address in which he has announced the partial mobilisation of forces in Russia. He said that the army was facing the military operations of the collective west on a frontline of over 1,000km in Ukraine. Those in the military reserves would be called up.

Putin also said Russia would give its full support to the referendums announced for this weekend in Luhansk, Donetsk, Kherson and Zaporizhzhia to join the Russian Federation. He accused the west of starting a war against Russia in Ukraine in 2014. “In its aggressive anti-Russian policy the west has crossed all lines,” the Russian president said. He accused the west of planning to destroy Russia and use nuclear blackmail.

Putin said he would use “all means available to us” and that those who are trying to use nuclear blackmail against Russia will find the tables can be turned against them. He explicitly said “I’m not bluffing.”

The proxy Russian authorities in four occupied areas of Ukraine – Donetsk, Luhansk, Kherson and Zaporizhzhia – had announced on Tuesday their intentions to hold referendums between 23-27 September on joining the Russian Federation, a move that could sharply escalate the war.

Ukrainian president Volodymyr Zelenskiy, speaking in a video address released early on Wednesday, said in relation to the referendums: “Our position does not change according to this noise or any other announcement”. Kyiv said the “sham” referendums were meaningless and vowed to “eliminate” threats posed by Russia, saying its forces would keep retaking territory regardless of what Moscow or its proxies announced. Zelenskiy will speak to the UN general assembly by video-link on Wednesday.

The White House rejected Russia’s plans to hold the referendums, adding that Moscow may be making the move to recruit troops in those areas after suffering extensive losses on the battlefield. Jake Sullivan, president Joe Biden’s national security adviser, called the referendums an affront to principles of sovereignty and territorial integrity.

Several world leaders have said they will not recognise any referendums or new annexations of Ukrainian territory, with French president Emmanuel Macron calling the plan a “parody”.

Any referendums on joining Russia in Russian-occupied Ukrainian territories would destroy any remaining window for talks between Kyiv and Moscow, Ukrainian publication Liga.net cited the Ukrainian president’s office spokesman as saying on Tuesday. “Without the referendums, there is still the smallest chance for a diplomatic solution. After the referendums - no,” Liga.net quoted Serhiy Nykyforov as saying.

Earlier this week Putin condemned what he described as US efforts to preserve its global domination, saying they are doomed to fail. Speaking while receiving credentials from foreign ambassadors to Moscow, Putin said: “The objective development toward a multi-polar world faces resistance of those who try to preserve their hegemony in global affairs and control everything – Latin America, Europe, Asia and Africa.”

With Germany’s gas storage facilities now at just over 90% capacity, Robert Habeck, the economy minister, said Germany now stands “a good chance” of getting through the winter. Germany is ahead of its goal to have the subterranean stores 95% full by the start of November.

The general staff of Ukraine’s armed forces said on Tuesday evening that its operations in Donetsk near the towns of Bakhmut and Avdiivka caused Russia to suffer “significant losses”. But Russia shelled those towns and dozens more in north-eastern and southern Ukraine, the general staff said.

US senators on Tuesday proposed that Biden’s administration use secondary sanctions on international banks to strengthen a price cap G7 countries plan to impose on Russian oil. Democratic Senator Chris Van Hollen and Republican Senator Pat Toomey announced a framework for legislation to impose the secondary sanctions, which would target financial institutions involved in trade finance, insurance, reinsurance and brokerage of Russia oil and petroleum products sold at prices exceeding the cap.

Reuters and Agence France-Presse contributed to his report