London, Aug 29 (IANS): Ambassadors of the 28 NATO members Friday met in an emergency meeting in Brussels to discuss the crisis in eastern Ukraine, as the West stepped up its accusations of direct Russian involvement in the conflict.

On Thursday, NATO released satellite images it said showed Russian forces inside Ukraine, and said more than 1,000 troops were operating there, BBC reported.

Russia has denied all accusations of sending troops to conflict-hit eastern Ukraine.

Heavy fighting was continuing Friday near the strategic port of Mariupol, on the Azov Sea.

Rebel forces were trying to capture the city but were failing due to the unrelenting defence put up by the Ukrainian government troops.

The advance has raised fears that the Kremlin might seek to create a humanitarian corridor between Russia and Crimea -- a territory annexed by Russia from Ukraine in March.

Rebels were also reported to have surrounded government soldiers in several places near the city of Donetsk.

Ukrainian forces near the town of Ilovaysk said they were cut off and have been urgently asking for supplies and reinforcements.

According to a UN report, at least 2,593 people have been killed and 5,043 injured in the conflict between April and Aug.

The report said that 155,800 people have fled elsewhere in Ukraine while at least 188,000 have gone to Russia.