KIEV, Ukraine (AP) -- Ukraine plans to begin pulling back heavy weaponry from the front lines of its fight with Russia-backed separatist rebels on Sunday, in accordance with a peace plan whose initial step was a cease-fire that is still being violated, a military spokesman said.
Ukrainian military spokesman Col. Andriy Lysenko told a briefing that the withdrawal was to begin, but did not give further details.
Rebel spokesman Eduard Basurin said the pullback from both sides is to take place between Sunday and March 7, but he did not specify whether rebels had made any moves yet. There was no immediate confirmation that the withdrawal had begun.
Both sides are to pull back their big guns and rockets from 25 to 70 kilometers (15 to 43 miles) away from the conflict line -- depending on the weapons' size -- creating a buffer zone of between 50 and 140 kilometers (31-87 miles).
The buffer zone was a main element of a peace agreement worked out in marathon negotiations 10 days ago in Minsk, Belarus. It also calls for a full exchange of war captives. Late Saturday, 139 Ukrainian soldiers and 52 rebels were exchanged; it remains unclear how many prisoners in total are on each side and when other swaps might take place.
The cease-fire that was the first element of the Minsk plan was called into effect last Sunday.
Ukrainian said Russia-backed separatists violated the cease-fire a dozen times during the night with artillery and rocket attacks and an attempt to storm a Ukrainian encampment. Lysenko said one serviceman was killed and three wounded over the past day.
Explosions were heard in the main rebel-held city Donetsk around dawn on Sunday and a rebel website says several buildings in the city were damaged by artillery.
Despite the reported violations, the level of firing appeared to be far lower than a week ago when a cease-fire was called.
Among the attacks reported by the Ukrainian military was an attempt to storm positions in the village of Shyrokyne near the port city of Mariupol. That city remains of strategic concern to Ukraine because rebel seizure of it could help establish a land corridor between mainland Russia and the Russia-annexed Crimean peninsula.