Washington worries about escalating the situation, by sending jets into airspace contested by Russia
The United States say a Polish plan to provide fighter jets to Ukraine is 'not tenable.'
It suggested passing them on through a US-NATO base in Germany.
But Washington's worried about escalating the situation by sending planes from one of their sites directly into airspace contested by Russia.
In Ukraine, the south-eastern city of Enerhodar says a temporary ceasefire is in place - and the evacuation of civilians can go ahead.
Last night Moscow said its troops would again stop firing this morning, to setup humanitarian corridors.
An estimated figure of 5,000 people escaped from Sumy in the north-east yesterday - but a ceasefire did not hold in Mariupol in southern Ukraine.
The Red Cross describes the situation there as apocalyptic – with people running out of electricity, food and drinking water.