(Bloomberg) -- Vladimir Putin vowed his annexation of four occupied regions in Ukraine is irreversible, as the Russian president formalized Europe's biggest land grab since World War II and accused the West of trying to subjugate his country.
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"They will become our citizens forever," he told officials in a Kremlin ceremony Friday before he and Moscow-installed leaders signed annexation documents. He demanded Ukraine stop fighting and begin talks, but refused to negotiate about the territories he's absorbing. "We will use all means available to us to defend our lands," he said.
The United Nations has denounced the annexation as illegal. Ukrainian President Volodymyr Zelenskiy condemned it, vowing to press ahead with his counteroffensive. Dialog "is impossible with this Russian president," he said.
The US added hundreds of Russian officials, including Putin's top central banker and energy chief, to its sanctions list. "We will rally the international community to both denounce these moves and to hold Russia accountable," President Joe Biden said in a statement, vowing to continue to provide military aid to Ukraine. The European Union also planned new restrictions.
With his troops losing ground to Kyiv's attacks, Putin has been struggling to revive his seven-month-old invasion. He's ordered the mobilization of 300,000 reservists to shore up his battered army, triggering an exodus of Russians trying to avoid being sent to the front.
Putin has brandished the threat of using nuclear weapons to protect Russia's sovereignty over the newly acquired territories, drawing warnings of harsh retaliation from the US and its allies.
In his speech Friday, Putin didn't mention nuclear weapons specifically with regard to the defense of the annexed areas. But he denounced the US for using them on Japan in 1945. "The United States is the only country in history that has used nuclear weapons," he said. "Creating, by the way, a precedent."
Before the address, Kremlin spokesman Dmitry Peskov called the talk of nuclear escalation "irresponsible" and declined to say whether attacks on the annexed territories may meet the standard for using the weapons set out in Russia's military doctrine.
Putin is laying claim to about 15% of Ukraine's land area, making the move the largest forced annexation in Europe since World War II.
"This is comparable to Austria and Belgium combined. Or Denmark, Belgium and the Netherlands combined. Or 30% of Germany," Estonian Prime Minister Kaja Kallas said in a statement. "Russia tries to rewrite the map of Europe."
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Peskov said Putin has no plans to visit the annexed zones at present, Tass reported.
The Russian leader devoted much of the 37-minute address to reiterating his denunciations of the US and its allies for allegedly trying to turn Russia into a "colony. " Lashing out at what he described as the "pure satanism" of Western liberal values, he said Russia has its own views on the issues of gender and family.
The signing ceremony ended with a smiling Putin holding hands with the four regions' Kremlin-installed chiefs as he joined in chants of "Russia" in the hall. Later, he took the stage at a celebration concert authorities held on Red Square, saying, "Victory will be ours!"
Russian officials are moving quickly to try to formalize their grip on the occupied areas, promising to issue passports and to appoint senators representing the regions in the upper house of parliament.
In an apparent sign of the hastiness of the latest moves, Kremlin spokesman Peskov said he wasn't immediately able to say whether Russia will be annexing all of the territory of the Kherson and Zaporizhzhia regions or just the areas held by its troops. He said the agreements Friday will cover the full areas of the Donetsk and Luhansk regions, though Ukraine still controls parts of those.
Kyiv's allies in the US and Europe have vowed to continue billions of dollars in financial and military aid to support Ukraine's drive to oust Russian forces. Ukrainian troops closed in on Lyman on Friday, a key transport hub in the Donetsk region, with some analysts suggesting a large number of Moscow's forces are at risk of being surrounded in the area.
Russia has also stepped up threats to European energy supplies in an effort to sap support there for Ukraine. State gas giant Gazprom warned it may shut off the last pipeline carrying its gas to clients in western Europe, while leaks discovered in the Nord Stream links under the Baltic Sea have raised suspicions of sabotage and fears of attacks on other infrastructure.
Putin blamed "Anglo-Saxons" for sabotage of the pipelines, without citing any evidence. The US rejected the allegation as "absurd."
A Russian missile strike killed at least 25 civilians near Zaporizhzhia early Friday, Ukrainian officials said. The city is one that Russia has included in the territory it claims to have annexed, although its forces have never reached it. The victims had been lining up in a convoy to travel toward the Russian-occupied zone to evacuate relatives, Ukraine said.
(Updates with Biden quote from fourth paragraph)
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