Poland is urging the U.S. to respond to Russian President Vladimir Putin's "mocking" response to President Donald Trump's attempts to secure peace deal by striking civilians.

Russia said two of its missiles had hit a meeting of Ukrainian military officers on Sunday in the city of Sumy, where Ukraine said Russian strikes had killed 34 people and wounded 117. Russia's defence ministry accused Ukraine of using civilians as human shields by placing military facilities and holding events involving soldiers in the centre of a densely populated city.