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.

Social Media Could Change Forever If Meta Loses US Legal Battle, Says Experts
Efforts To Achieve Peace Plan For Gaza Continue As US Meet Middle East Mediators
US Military Fire On Ship In Gulf Of Oman
Over 250 People Now Confirmed Dead Following Devastating Earthquake In Colombia
Rescue Operation Continues After 160 Dead In Colombian Earthquake
Six Killed In School Shooting Near Bangkok In Thailand
Reports Of Iran And Oman Working Towards Deal To Reopen Strait Of Hormuz
EU Home Affairs Ministers Meet To Discuss Protection Of Borders From Illegal Migration