Kiev: A bomb blast killed two at a march in east Ukraine on Sunday on the first anniversary of the ouster of the country’s Russia-friendly president, a gruesome counterpoint to the hopes spawned by a cease-fire agreement more than a week ago.

An exchange of prisoners this weekend and acknowledgment by both sides of a commitment to pull back heavy weapons are promising signs that peace may yet prevail, although sporadic exchanges of hostilities between government and separatist forces have yet to subside entirely.

Ukraine’s Interior Ministry said the blast at a march in the eastern city of Kharkiv to mark the ouster of President Viktor Yanukovych was due to an “unknown explosive device” and was considered a terrorist act.

A police officer was one of the dead and about a dozen people were injured, the ministry said.

A spokesman for the national security service, Markian Lubkivskiy, said four suspects had arrested for the explosion and for planning other attacks, Interfax-Ukraine news agency reported.

The violence comes as Ukraine continues to be riven by tension and bloodshed stemming from Yanukovych’s fall.

The Ukrainian parliament voted February 22, 2014 to remove him, following months of increasingly violent protests in the capital, Kiev.

The Crimean peninsula, where residents largely regarded his downfall as a coup, was annexed by Russia a month later.

Then armed rebels opposed to the new authorities in Kiev took over large parts of two regions bordering Russia, setting off a war that has killed more than 5,600 people.

A peace plan envisioning a cease-fire and pullback of heavy weapons was signed February 12.

Ukraine planned to begin withdrawing heavy weaponry from the front lines today, Ukrainian military spokesman Colonel Andriy Lysenko told a briefing, but gave no details.

Rebel spokesman Eduard Basurin said the pullback from both sides is to take place between today and March 7, but he did not say whether rebels had made any moves yet. There was no immediate confirmation that the withdrawal had begun.