President Biden made an unannounced visit to Kyiv on Monday, an audacious and somewhat risky trip aimed at expressing solidarity with Ukrainians as Russia's invasion of their country heads into a second year.

Biden met with Ukrainian President Volodymyr Zelenskyy and announced a half a billion dollars of additional assistance to Ukraine — and said there would be new sanctions on Russia — with details to be released in coming days.

"One year later, Kyiv stands. And Ukraine stands. Democracy stands," Biden said.

Biden's visit comes as Russian forces make a new push to take control of Ukraine's eastern Donbas region, which Russia illegally annexed last September.

Biden had been slated to travel to Warsaw this week to mark the anniversary of the war and to hold a series of meetings with central European allies.

Instead, he secretly left Washington early on Sunday morning. Details of how he got to Ukraine were not immediately available due to security concerns. Kyiv has been the target of Russian missile and drone strikes, including as recently as Feb. 10.

Only three officials as well one reporter and one photographer traveled with Biden. A small group of reporters already inside Ukraine — including NPR's Joanna Kakissis — joined Biden after his arrival at 8 a.m. local time.

Zelenskyy called it "a huge moment for Ukraine" and "a historical moment for our country."

Biden met with Zelenskyy at Mariinsky Palace. Then, the two leaders walked together outside St. Michael's cathedral in central Kyiv. Air raid sirens were heard across the city as they left the church.

"I thought it was critical that there not be any doubt, none whatsoever, about U.S. support for Ukraine in the war," Biden said, emphasizing bipartisan support in Congress for Ukraine.

Biden has marshalled international support for Ukraine, sending billions of dollars of weapons and economic aid to Kyiv and uniting allies and partners around economic sanctions meant to punish Moscow for the invasion.The U.S. Congress appropriated more than $112 billion in defense, economic and humanitarian aid last year.

But with no end to the war in sight, polls show a growing number of Americans are concerned about how much money has gone to the war — and some Republican budget hawks have said they would like to curtail the spending.

This is a breaking news story. It will be updated as more details are made available. [Copyright 2023 NPR]