Separatist rebels have launched a push using tanks and artillery towards Ukrainian government positions west of the big regional city of Donetsk in an escalation of the conflict in the east, the Kiev military said on Wednesday.

"At 3 a.m. (2000 ET) the enemy launched a massive bombardment on our positions near Maryinka and Krasnogorivka including from heavy weapons. They used tanks and artillery," military spokesman Andriy Lysenko told a briefing.

"The enemy is trying to advance. Ukrainian forces are holding off all the attacks," he said.

Maryinka, which had a pre-conflict population of around 9,900, is 15 kms (9 miles) west of the rebel stronghold of Donetsk.

The separatist press service DAN quoted senior rebel commander Eduard Basurin as saying clashes were still going on as of 1.45 p.m. (0645 ET) without giving further details. He accused government troops of firing artillery at separatist forces.