President Donald Trump on Monday sought to increase pressure on Russian President Vladimir Putin in a bid to secure an end to Moscow's full-scale invasion of Ukraine.

President Donald Trump says he's "very disappointed" in Russian President Vladimir Putin following massive Russian missile strikes on Ukraine that prompted both Kyiv and Poland to scramble for fighter jets.

Earlier this month, Trump set a 50-day deadline for Russia to accept a ceasefire. Failure to do so, the president said, would prompt punishing new economic measures, among them secondary sanctions on nations doing business with Moscow.