Intense artillery exchanges between Ukrainian government forces and Russian-backed separatists persisted Monday around a strategic town in eastern Ukraine - fighting that threatens to dash a cease-fire deal brokered by European leaders last week.

Under the cease-fire agreement negotiated by the leaders of Ukraine, Russia, Germany and France, the warring sides are to begin withdrawing heavy weapons from the front line Tuesday. That plan already looks at risk, with the rebels saying they are not satisfied that conditions are in place for the process to go ahead.

Despite the cease -fire that went into effect early Sunday morning, five Ukrainian troops were killed and 25 were wounded in the past 24 hours, Ukrainian military spokesman Andriy Lysenko said Monday.