A defiant Vladimir Putin proclaimed Russia's annexation of a swathe of Ukraine in a pomp-filled Kremlin ceremony, promising Moscow would triumph in its "special military operation" against Kyiv even as some of his troops faced potential defeat.
The Russian president's proclamation of Russian rule over 15% of Ukraine – the biggest annexation in Europe since World War Two – was roundly rejected by Western countries, with the United States and Britain announcing new sanctions.
It comes as Russian forces in one of the four regions being annexed face being encircled by Ukrainian troops.
In one of his toughest anti-American speeches in more than two decades in power, Putin signalled he was ready to continue what he called a battle for a "greater historical Russia," slammed the West as neo-colonial and as out to destroy his country, and without evidence accused Washington and its allies of blowing up the Nord Stream gas pipelines.
The four Ukrainian regions that he said Russia was absorbing had made a historic choice, he said.
"They have made a choice to be with their people, their motherland, to live with its fate, and to triumph with it. Truth is on our side. Russia is with us!" Putin told his country's political elite, who had gathered in one of the Kremlin's grandest halls to watch him sign the annexation documents.
"People living in Luhansk, Donetsk, Kherson region and Zaporizhzhia region are becoming our compatriots forever."
"We will defend our land with all our strength and all our means," he added, calling on "the Kyiv regime to immediately cease hostilities and return to the negotiation table".
Putin said the United States had set a precedent when it had dropped two atomic bombs on Japan in 1945, but stopped short of issuing new nuclear warnings against Ukraine himself, something he has done more than once in recent weeks.
US Secretary of State Antony Blinken said the United States had not yet seen Russia take any action that suggested it is contemplating the use of nuclear weapons, despite what he called Putin's "loose talk".
The annexation ceremony culminated in Putin, 69, chanting "Russia! Russia!" as he clasped the hands of the Russian-backed officials he wants to run the annexed regions, which Ukraine is fighting to win back.
Thousands of people, some of them clutching Russian flags, then packed into Moscow's Red Square to hear celebratory pop music. Putin told the crowd: "Victory will be ours!"
Ukraine NATO bid
US President Joe Biden said new US sanctions would hurt those who provided political or economic support to the annexation drive.
"We will rally the international community to both denounce these moves and to hold Russia accountable. We will continue to provide Ukraine with the equipment it needs to defend itself, undeterred by Russia's brazen effort to redraw the borders of its neighbour," Biden said in a statement.
NATO chief Jens Stoltenberg accused Putin of provoking "the most serious escalation" of the war since it began on Feb 24, but said he would not succeed in deterring the alliance from supporting Kyiv.
In Ukraine, President Volodymr Zelenskiy said he was only ready for peace talks if and when Russia got a new president.
He also announced that Ukraine was formally applying for fast-track membership of NATO, something Moscow fiercely opposes, and accused Russia of redrawing borders "using murder, blackmail, mistreatment and lies".
He said however that Kyiv remained committed to the idea of co-existence with Russia "on equal, honest, dignified and fair conditions".
"Clearly, with this Russian president it is impossible. He does not know what dignity and honesty are. Therefore, we are ready for a dialogue with Russia, but with another president of Russia," Zelenskiy said.