At a ceremony denounced by Ukraine as a "Kremlin freak show", Russian President Vladimir Putin will proclaim the annexation of four Ukrainian regions on Friday, escalating his seven-month war and taking it into an unpredictable new phase.

Putin will preside over a treaty-signing on "the entry of new territories into the Russian Federation", three days after the completion of hastily staged referendums in which Moscow's proxies in the occupied regions claimed majorities of up to 99% in favour of joining Russia.

Ukraine and Western governments described those votes as bogus, illegitimate and conducted at gunpoint. "The Kremlin's sham referenda are a futile effort to mask what amounts to a further attempt at a land grab in Ukraine," U.S. Secretary of State Antony Blinken said on Thursday.

Moscow says people chose freely to return to their "historic motherland".

The ceremony - eight years after Russia seized Crimea from Ukraine following an invasion and a similar vote - will take place at 3 p.m. (1200 GMT) in the columned St George's Hall of the Grand Kremlin Palace, where marble plaques engraved in gold commemorate Russian military heroes.

But despite the triumphal setting, the annexation of the Donetsk, Luhansk, Zaporizhzhia and Kherson regions comes at a perilous moment for Putin.

After months of grinding, attritional warfare, Ukraine seized the initiative this month by routing Russian forces in the northeastern Kharkiv region. Putin last week declared an unpopular partial mobilisation, prompting thousands of fighting-age men to flee the country. Even staunch Kremlin allies have criticised the chaotic nature of the call-up, and Putin himself said on Thursday that "all mistakes must be corrected".

NUCLEAR THREAT

While it holds the vast majority of Luhansk and Kherson regions, Russia controls only about 60% of Donetsk and 70% of Zaporizhzhia, where fighting has raged close to Europe's biggest nuclear plant.

The hurried annexations mean front lines will now run through territory that Russia is declaring as its own, and which Putin has said he is ready to defend with nuclear weapons if necessary.

Some Western politicians called that a bluff - something Putin explicitly denied. The United States says it has warned Russia of catastrophic consequences if it did use a nuclear weapon.

Ukrainian presidential adviser Mykhailo Podolyak said on Thursday that the Kremlin event was a "freak show", and legally meaningless. "Non-existent entities cannot enter a country which is disintegrating," he said on Twitter.

United Nations Secretary-General Antonio Guterres said if Moscow proceeded, it would have "no legal value and deserves to be condemned".

Kirill Stremousov, a Russian-installed official in Kherson region, published a video of himself next to Red Square, declaring: "Victory is ours. We are Russia."

The Kremlin has not yet said whether Putin will attend a celebratory concert on the square on Friday evening. He is due to address parliament separately at a later stage, paving the way for it to ratify the annexation process on or before Oct. 7, when he marks his 70th birthday.

(Writing by Mark Trevelyan; editing by Jonathan Oatis)

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