U.S. President Donald Trump's Ukraine envoy Keith Kellogg began talks in Kyiv on Monday on security and sanctions against Russia. That's a day after the U.S. president said he would send Patriot air defence missiles to Ukraine.

The president has become increasingly exasperated with Vladimir Putin and has repeatedly laid into the Russian leader for prolonging the Ukraine war.

President Donald Trump is scheduled to welcome NATO Secretary-General Mark Rutte to the White House on Monday.