Vladimir Putin said Russia’s armed forces would call up its reserves immediately to support its invasion of Ukraine and indicated Moscow would probably annex large swaths of Ukrainian territory.

In a televised address to the nation on Wednesday, the Russian president announced “partial mobilisation” ahead of heavily stage-managed votes in four occupied regions of Ukraine to join Russia.

Putin’s decision dramatically raises the stakes for the war more than six months since he first sent troops into Ukraine in late February, defining it as an existential struggle for Russia’s survival against what he described as a hostile west.

The Russian president claimed the west wanted to “weaken, divide, and destroy Russia” and made a thinly veiled threat to use nuclear weapons if Ukraine continued its offensive operations.

He accused the west of using “nuclear blackmail” against Russia and vowed: “If its territorial integrity is threatened Russia will use all the means at its disposal. This is not a bluff.”

By effectively annexing south-eastern Ukraine, Putin said Russia would “use all the means at our disposal to defend the country and the people” — carrying the threat that Russia would deploy nuclear weapons if its efforts were deterred.

Putin’s decision to annex areas of occupied Ukraine and threat to use “all means” to defend Russia was a calculated move to test western resolve in support of Kyiv, western officials said.

The rapid annexation plan and partial mobilisation of Russian society was a sign of Putin’s weakness, they said. They added that allies that had provided billions of dollars of weapons to Ukraine to defend itself against Russia’s invasion would continue to do so as Kyiv sought to liberate more territory in the country’s east currently held by Russian forces.

“Sham referenda and mobilisation are signs of weakness, of Russian failure,” said Bridget Brink, the US ambassador to Ukraine, in response to Putin’s announcement. “The United States will never recognise Russia’s claim to purportedly annexed Ukrainian territory, and we will continue to stand with Ukraine for as long as it takes.”

Russian defence minister Sergei Shoigu, in a pre-recorded statement aired after Putin’s announcement, said Moscow would only call up reserves, rather than deploying the conscript army. This would add 300,000 people to Russia’s fighting force, he said.

Men will be called up “specifically from the reserves,” Shoigu said.

He said these would be people who have previously served, have experience of combat, and have some military specialisation that is needed by the armed forces. “These are not people who’ve never seen or heard anything about the army,” he said.

“Let me pre-empt questions. We’re not talking about the mobilisation of any students . . . They can calmly keep going to class,” Shoigu said. He claimed that after the reserves were called up, Russia would still have only used up 1 per cent of its mobilisation potential.

Russia appeared to acknowledge that advanced western weaponry such as the US-manufactured Himars rocket launcher system had begun to turn the tide on the battlefield.

“We are not at war with Ukraine, but with the collective west,” Shoigu said in a state television interview following Putin’s speech.

Russia’s invasion has badly faltered, with invading forces taking heavy casualties before retreating from central Ukraine in the spring and then ceding huge swaths of territory in the eastern Kharkiv region following a stunning Ukrainian counter-offensive earlier this month.

Putin said Moscow would back votes to join Russia in the parts of Ukraine’s Donetsk, Luhansk, Kherson, and Zaporizhzhia regions that are currently under its control, which are scheduled for this weekend.

The result of the “referendums” is effectively a foregone conclusion, with the Kremlin in charge of the vote and insisting more than 90 per cent of the local population wants to join Russia.

Russia does not control any of the regions in full, while many locals have fled to both Ukraine and Russia to escape the fighting.

Ukraine’s western allies have said they will not recognise the results of the vote, which the US has described as a “sham”.

Putin framed the decision as a move to protect Russian-speakers in south-eastern Ukraine from Kyiv’s recent advances.

“Russia can’t give up people close to her to be torn apart by executioners and fail to respond to their desire to determine their own fate,” he said.