Russian President Vladimir Putin has signed decrees to formally seize four Ukrainian territories partially occupied by Moscow as he escalates his failing seven-month invasion.

At a lavish ceremony on September 30 in the opulent white-and-gold St. George's Hall in Moscow, Putin signed the decrees -- which the Kremlin calls "accession treaties"-- to incorporate the Luhansk, Donetsk, Kherson, and Zaporizhzhya regions as hundreds of members of the nation's elite applauded.

Putin claimed that the people had "made a choice" in referendums widely seen as having been conducted at the barrel of a gun.

Several European countries, including Sweden, Poland, Germany, and Britain, joined the United States in immediately condemning the move as illegal.

U.S. President Joe Biden called it a "fraudulent attempt" to annex sovereign Ukrainian territory, which he said was a flagrant violation of international law. He said in a statement that new U.S. sanctions would hurt those who provided political or economic support to the annexation drive.

During a 30-minute speech that preceded the signing and was filled with grievances toward the West, Putin hinted at the use of nuclear weapons to defend the four regions his forces are trying to hold, saying Russia would defend them "by all the means we possess."

The ceremony comes three days after the completion of Kremlin-orchestrated referendums on joining Russia that were dismissed by Kyiv and the West as a bare-faced land grab, held at gunpoint and based on lies.

Putin rushed to carry out the so-called referendums and the signing of the "accession treaties" amid a successful counteroffensive by Ukraine that has pushed Moscow's forces back and raised the specter of a Russian defeat.

As Putin signed the documents, Ukrainian forces were on the verge of another major victory in the Donbas.

By seizing the regions, Putin is seeking to justify not only the use of weapons of mass destruction but also his recent mobilization of citizens on the grounds to defend Russian "territory," experts say.

Putin’s September 21 decision to call up 300,000 reservists has sparked protests across the country.

During his speech, Putin called on Ukraine to lay down its arms, falsely accusing Kyiv of starting the war in the eastern provinces in 2014, one of the many historical inaccuracies he voiced.

The Kremlin instigated the war in the Donbas when it backed separatists and sent in irregular forces following the ouster of Kremlin-leaning Ukrainian President Viktor Yanukovych in February of that year.

Putin claimed he was "ready" for peace talks but said the annexation of the four regions would not be on the table, a proposition unacceptable to Ukraine and akin to escalation.

The four regions together with Crimea make up around 20 percent of Ukraine, including some of its most industrialized territory.

Ukrainian President Volodymyr Zelenskiy, whose forces in recent weeks have launched a successful counteroffensive that has clawed back some territory, promised a strong response to the move and summoned his defense and security chiefs for an emergency meeting.

He announced afterward that Ukraine has applied for accession to NATO under an accelerated procedure.

He said Putin's statements about occupied or partially occupied regions of Ukraine "joining Russia" are an attempt to steal what does not belong to Russia.

Zelenskiy said earlier on the Telegram messaging app that he and the military chiefs discussed supplies of weapons for the country's armed forces, as well as Russia's possible further plans following its invasion of Ukraine.

Prior to the ceremony, the United Nations and Western leaders denounced Russia's plans to annex the four regions.

British Prime Minister Liz Truss criticized Putin for showing "clear disregard for the lives of the Ukrainian people he claims to represent."

German President Frank-Walter Steinmeier also condemned the referendums held in the four Ukrainian territories and their imminent seizure by Russia.

Steinmeier made this statement at a medal ceremony to mark German Unity Day in Berlin on September 30. (KB/RFE-RL)