Nato officials are holding an emergency meeting to discuss the crisis in eastern Ukraine, as the West steps up its accusations of direct Russian involvement in the conflict, reports GHN based on BBC.
On Thursday Nato released satellite images it said showed Russian forces inside Ukraine. and said more than 1,000 troops were operating there.
Russia denies sending troops.
Pro-Russian rebels have gained ground recently. Nearly 2,600 people have been killed since April, the UN says.
Heavy fighting is continuing near the strategic port of Mariupol, on the Azov Sea. Rebel forces are trying to capture the city but Ukrainian government troops are digging in.
On Thursday the separatists seized the nearby town of Novoazovsk.
The advance has raised fears that the Kremlin might seek to create a land corridor between Russia and Crimea - a territory annexed by Russia from Ukraine in March.
Rebels are also reported to have surrounded government soldiers in several places further north, near the city of Donetsk.
Ukraine forces near the town of Ilovaysk say they are cut off and have been urgently asking for supplies and reinforcements.