Russia was even more diplomatically isolated Saturday after President Vladimir Putin annexed four Moscow-held areas of Ukraine with Kyiv condemning the move and vowing to retake the territories.
Putin staged a grand ceremony in the Kremlin on Friday to celebrate the annexation, hours after shelling killed 30 people in Ukraine's southern region of Zaporizhzhia.
"I want to say this to the Kyiv regime and its masters in the West: People living in Lugansk, Donetsk, Kherson and Zaporizhzhia are becoming our citizens forever," Putin said.
Washington announced "severe" new sanctions against Russian officials and the defence industry, and said G7 allies support imposing "costs" on any nation that backs the annexation.
Ukrainian President Volodymyr Zelensky immediately urged the US-led military alliance NATO to grant his country fast-track membership.
He also vowed never to hold talks with Russia as long as Putin was in power.
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US President Joe Biden condemned Friday's ceremony in Moscow as a "sham routine" and pledged to continue backing Kyiv.
NATO chief Jens Stoltenberg slammed the annexation as "illegal and illegitimate" but remained non-committal after Ukraine said it was applying to join the Western alliance.
The United States and Canada voiced support for Ukraine's membership but steered clear of promises to fast-track it.
Turkey on Saturday said Russia's annexation was a "grave violation of the established principles of international law".
Nuclear plant boss detained
Despite warnings from Putin prior to the annexation that he could use nuclear weapons to defend the captured territories, Ukraine's Foreign Minister Dmytro Kuleba said Kyiv would "continue liberating our land and our people".
Kuleba also said Ukraine brought the annexations to the International Court of Justice and urged the Hague-based court to hear the case "as soon as possible".
US National Security Advisor Jake Sullivan said Friday that Washington would announce an "immediate" new weapons shipment for Kyiv next week.
Sullivan also said that while there is a "risk" of Putin using nuclear weapons, there is no indication that he would imminently do so.
Hours ahead of the annexation ceremony, an attack in Zaporizhzhia in the south killed at least 30 people and wounded dozens as civilians were preparing to leave to pick up relatives, Ukrainian officials said.
Bodies in civilian clothes were strewn across the ground after the attack and windows of cars blown out.
On Saturday, Ukraine's nuclear agency said a "Russian patrol" detained the director general of the Moscow-held Zaporizhzhia nuclear power plant.
Ihor Murashov was detained on Friday as he was leaving the plant and was "driven in an unknown direction" while blindfolded, Energoatom said.
Zaporizhzhia -- Europe's largest nuclear energy facility -- has been at the centre of tensions in recent weeks after Moscow and Kyiv accused each other of strikes on and near the plant, raising fears of an atomic disaster.
Crucial land corridor
The four annexed territories create a crucial land corridor between Russia and the Crimean Peninsula, annexed by Moscow in 2014.
Together, the five regions make up around 20 percent of Ukraine, where forces in recent weeks have been clawing back territory.
Zelensky on Friday hailed the "significant results" from Ukraine's counteroffensive in the east.
Ukrainian forces were on the doorstep of Lyman in Donetsk, which Moscow's forces pummelled for weeks to capture this summer.
"Lyman is partially surrounded," said Denis Pushilin, the pro-Moscow leader in Donetsk, adding later on social media that Russian forces were holding out "with the last of their strength".
Russia on Friday vetoed a UN Security Council resolution condemning the annexation of the regions, while China, India, Brazil and Gabon abstained.
Although Russia's veto was a certainty, Western powers had hoped to demonstrate Moscow's growing isolation on the world stage and will now take the condemnation effort to the General Assembly, where every nation has a vote and none can kill a resolution.
At a UNESCO meeting in Mexico City on Friday, representatives of dozens of countries walked out as Russia took the floor, symbolically condemning the invasion of Ukraine.