Western leaders say they are seeing "the most serious escalation" since the war in Ukraine began. But those in Moscow say they have achieved a victory. On Friday, President Vladimir Putin declared four regions of eastern Ukraine to be a part of Russia.

Putin gathered with thousands of people at Moscow's Red Square to celebrate the annexation of Donetsk, Kherson, Luhansk, and Zaporizhzhia.

He said, "People turned out for the referendums and made this choice -- to be with their historic homeland, with Russia." He added that Russian troops will defend those territories by all forces and means.

However, Ukrainian President Volodymyr Zelenskyy called the takeover a criminal act.

He said, "Russia tries to steal what doesn't belong to it; it wants to rewrite history and redraw borders using murder, blackmail, torture, and lies. Ukraine will not allow this."

On Friday, Zelenskyy formally signed a document to join NATO. He said the application is under an "accelerated procedure."

NATO Secretary General Jens Stoltenberg said that the door is always open for Ukraine.

He said, "Every democracy in Europe has the right to apply for NATO membership, and NATO allies respect that right."

He added that any decision to admit new countries requires the consensus of all 30 members. But he said NATO's commitment to support Ukraine