STORY: Biden arrived in the Polish capital Warsaw late on Monday (February 20) after a surprise visit to Kyiv just days ahead of the anniversary of Russia's invasion of Ukraine on February 24, 2022.

Putin backed away from the New START arms control treaty - a 2010 agreement that limits the number of Russian and U.S. deployed strategic nuclear warheads - and warned that Moscow could resume nuclear tests.

"It is a big mistake," Biden said of Putin's decision as he headed into the meeting with eastern European allies.

In central Warsaw, a small group of demonstrators gathered to call on Biden to deliver fighter aircraft to Ukraine.

Around a dozen demonstrators massed opposite the hotel where President Biden was staying, bringing with them a large banner reading "Mr. Biden, send F-16 to Ukraine."