LONDON - President Vladimir Putin will sign documents on Friday proclaiming Russia's annexation of four Ukrainian regions, as Moscow rushes to lock in territorial claims that the Ukrainian army is threatening to reverse on the battlefield.
The move, one of the legal steps Russia says will lead to formal annexation of 15% of Ukraine's territory, confirms that Putin is doubling down on his war against Ukraine despite suffering a major military reversal this month.
The annexation, after what Kyiv and Western countries say were phoney referendums staged at gunpoint on Russian-held Ukrainian territory, has been rejected in the West as an illegal seizure of land captured in war.
Ukrainian President Volodymr Zelenskiy summoned his security and defence chiefs for an emergency meeting to be held on Friday, and promised a robust response to a step he says has killed off chances of reviving peace talks.
The votes "are worthless and do not change reality. The territorial integrity of Ukraine will be restored. And our reaction to recognition of the results by Russia will be very harsh," Zelenskiy said in a statement.
Washington and the European Union are set to impose additional sanctions on Russia over the annexation plan, and even some of Russia's close traditional allies, such as Serbia and Kazakhstan, say they will not recognise the move.
Putin's annexation ceremony will be held in one of the Kremlin's grandest halls with the pro-Russian figures Moscow considers to be leaders of the four Ukrainian regions -- Kherson, Zaporizhzhia, Donetsk and Luhansk. Russia says the referendums were genuine and showed public support for the move.
After days of speculation over exactly how Russia would mark the annexation, Putin's spokesman Dmitry Peskov confirmed some details of the ceremony on Thursday.
Agreements "on the accession of new territories into the Russian Federation" will be signed "with all four territories that held referendums and made corresponding requests to the Russian side," Peskov said.
Putin would deliver a major speech on the subject, he added.
A big concert will be held on Friday on Moscow's Red Square, where a tribune with giant video screens has already been set up, with billboards proclaiming "Donetsk, Luhansk, Zaporizhzhia, Kherson - Russia!"
Peskov did not say whether Putin would make an appearance at the concert. He did so at a similar event in 2014 after Russia proclaimed it had annexed Ukraine's Crimea region.
Putin publicly backed the annexation plans in a speech last week in which he also announced the call-up of hundreds of thousands of Russian reservists, and warned he could use nuclear weapons to defend Russian territory if necessary.
With tens of thousands of Russian men fleeing abroad to escape Putin's military call-up, Finland shut one of the few remaining routes to Europe, saying it would no longer let Russians enter by land with EU tourist visas.
The head of the upper house of the Russian parliament has said the chamber could consider the incorporation of the four regions on Oct. 4, three days before Putin's 70th birthday.
What Russia is billing as a celebration comes after Moscow has faced its worst setbacks of the war, with its forces routed in recent weeks in Ukraine's northeast.
Some military experts say Kyiv is poised to deliver another major defeat, gradually encircling the town of Lyman, Russia's main remaining bastion in the northern part of Donetsk province. Its fall could open the way for Ukrainian forces to launch attacks on swathes of territory that Russia now aims to annex.
"The situation looks increasingly precarious for Russian forces in Lyman as Ukrainian forces are about to cut them off," Carl Bildt, a former Swedish prime minister, said on Twitter.
"Another painful defeat for the Russian invasion forces is looming."
Kyiv has so far held back from disclosing details of the situation in Lyman. Russia's Defence Ministry said a day earlier that a Ukrainian offensive on Lyman had failed, with 70 Ukrainian soldiers killed.
Russian government officials have said that the four regions will fall under Moscow's nuclear umbrella once they have been formally incorporated into Russia.
The United States has unveiled a $1.1 billion weapons package for Ukraine that includes 18 High Mobility Artillery Rocket System (HIMARS) launchers, accompanying munitions, various types of counter drone systems and radar systems. The announcement brings the U.S. security aid to $16.2 billion.
Mystery continued to swirl over an apparent attack on the Nord Stream 1 and 2 pipelines under the Baltic Sea, built to carry Russian gas to Europe though already shut.
At least three explosions which sent hundreds of thousands of tonnes of methane gas jetting to the surface this week have left the pipes severely damaged, possibly permanently. Sweden's coast guard said it found a fourth leak.
Western countries have called the incidents sabotage while stopping short of openly ascribing blame. Russia, which has denied involvement, said the incidents looked like acts of state-sponsored terrorism and the United States stood to gain.
An EU official said the bloc's leaders would discuss the issue next week, adding that the apparent sabotage had changed the nature of the conflict in Ukraine fundamentally.
NATO said the explosions looked like a reckless and irresponsible act of sabotage, and that any deliberate attack against infrastructure of countries in the Western alliance would be met by a "united and determined response".
CNN, citing three sources, reported that European security officials had observed Russian navy support ships and submarines not far from the sites of the Nord Stream leaks beforehand.
Asked for a comment on the CNN report, Peskov said there had been a much larger NATO presence in the area.
(Reporting by Reuters bureaux; Writing by Andrew Osborn; Editing by Peter Graff)