A notorious warlord has been killed in a bombing in the rebel stronghold of Donetsk, separatist officials said.

A top NATO advisor said Ukrainian forces face "continual attacks," as video emerged from a purported battle with Russian-backed separatists that would be in violation of a three-month ceasefire.

Nearly 7,000 civilians have been killed in the war in eastern Ukraine between government forces and Russian-backed separatists, the nation's president said Friday.

Fighting is still raging on the outskirts of the rebel stronghold of Donetsk in eastern Ukraine despite peace talks this week.

Ukrainian government and Russian-backed separatist forces have both pulled back the bulk of their artillery and rocket launchers from the front line in the east, in compliance with a cease-fire deal, Ukraine's president said.

Ukraine's military says it is completing its pullback of heavy weapons under the terms of a peace agreement aimed at ending the war with separatist rebels that has killed more than 6,000 people.

A rebel-held city scarred by months of conflict in eastern Ukraine suffered more tragedy Wednesday when a methane gas explosion in a coal mine killed at least 24 workers.

Ukrainian troops held captive in the separatist stronghold of Donetsk began digging through the rubble Wednesday to retrieve the bodies of fellow soldiers killed last month.

After weeks of fierce, relentless fighting, the embattled rail hub of Debaltseve fell to rebel forces Wednesday in eastern Ukraine.

Artillery fire killed at least 12 civilians in the main rebel stronghold of Donetsk on Friday amid fierce fighting between pro-Russia separatists and government troops.