Annexation polls organized by Kremlin authorities in four regions of Ukraine mostly controlled by Russian forces were due to conclude on Tuesday amid looming threats from Moscow with nuclear weapons.

Kyiv and its allies have denounced the votes as a sham and said the West would never honor the election results, which are ramping up the stakes in Russia’s seven-month invasion.

Russian forces in Ukraine have suffered severe setbacks this month, both in the east and south of the country, which observers say has pushed President Vladimir Putin to speed up a vote to consolidate Moscow’s authority there.

Putin said Russia will use all available means to defend its territory, implying that after annexing the four regions, Moscow could use strategic nuclear weapons to repel Ukrainian attempts to retake the territory.

He also announced that Moscow would call up 300,000 reservists, a move that sparked some protests and caused Russian men fearing deployment to Ukraine to flee to neighboring countries.

Ukraine’s four Russian-held regions — Donetsk and Lugansk to the east, and Kherson and Zaporizhia to the south — announced they would hold the polls days before voting begins on Friday.

US President Joe Biden said the polls were a “sham” and little more than a “false pretext to try to forcibly annex parts of Ukraine”.

Even Moscow’s closest ally since the start of the invasion, Beijing, said after the votes were announced that both Russia and Ukraine should respect territorial integrity in the war.

Kremlin-backed leaders in the regions said preliminary results could be expected on Tuesday evening or in the following days.

Lawmakers are then expected to vote to formally annex the four territories, which would require Putin’s signature.

The so-called referendums follow a pattern used by Moscow in 2014 to annex the Crimean Peninsula from Ukraine after nationwide street demonstrations toppled the country’s pro-Kremlin president.

As in the past, observers regard the outcome of the election as a foregone conclusion. Election officials, in many cases escorted by Russian forces, carried the ballot boxes from door to door.

The UK government has sanctioned 92 Russian individuals and entities for their various voting roles ahead of the final day of voting.

“Mock referees held at the barrel of a gun cannot be free or fair and we will never honor their results,” Secretary of State James Cleverly said in a statement.

As fighting continued along Ukraine’s sprawling frontline, AFP journalists were led to the country’s latest suspected mass burial site at a shell-damaged and abandoned industrial chicken farm.

“I was told by the soldiers who came to our village that they saw a gravesite of soldiers, but they didn’t give the number,” said Lyudmyla Vakulenko, head of the Kozacha Lopan local administration.

The village is located in the eastern Kharkiv region, where dozens of towns and villages were recaptured during a counter-offensive by Ukrainian troops.