At least two houses blazed in the rural village of Spartak, which lies just north of Donetsk and adjacent to the airport, after they were hit by fire. A man whose house was struck by a shell said rebels had fired from a spot nearby, which appeared to have provoked a retaliatory attack from Ukrainian government troops. This pattern has been regularly observed in the nearly five-month-long military confrontation.
A group of rebel fighters in the village danced and drank Sunday morning in celebration after what they said was a successful assault on a Ukrainian military encampment in the vicinity. One said their group had captured eight government troops, although none of these captives could be seen.
The fighter, who provided only the nom de guerre Khokhol, freely acknowledged that the cease-fire was not being respected by either side.
"There was mortar shelling around 20 minutes ago here in Spartak," he said. "There is no cease-fire for anyone."
The truce signed on Friday appeared to be holding for much of the following day, but was shattered late Saturday by shelling on the outskirts of the southeastern port town of Mariupol, where Ukrainian troops retain defensive lines against the rebels. The city council said Sunday that one civilian was killed there and a serviceman wounded.
The volunteer pro-government Azov Battalion said on Facebook that their positions were also hit by Grad rockets, but did not give details.
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A local woman puts out the fire at her burning house after shelling in Donetsk, eastern Ukraine, Sun …
Mariupol is located on the coast of the Sea of Azov, 115 kilometers (70 miles) south of Donetsk. Rebels recently opened a new front on the coast, leading to fears that they were trying to secure a land corridor between Russia and the Crimean Peninsula, which Russia annexed in March.
Amnesty International on Sunday condemned all those engaged in the grinding conflict that according to U.N. estimates has claimed at least 2,600 civilian lives and forced hundreds of thousands out of their homes.
"All sides in this conflict have shown disregard for civilian lives and are blatantly violating their international obligations," Amnesty International Secretary General Salil Shetty said in a statement.
Blasts powerful enough to be heard in downtown Donetsk appeared to be coming from the direction of the airport early Sunday morning. The terminal, which has now been rendered little more than a burned-out husk, has been under the control of government troops since May and has come under unremitting attacks from Russian-backed separatist forces since then.
A rebel statement said Ukrainian forces fired on their positions in six locations on Saturday, including near the Donetsk airport, and several rebels were killed.
In nearby Spartak, resident Anastasia Ivanusenko, who has moved to Donetsk to escape the most intense fighting, learned her house had been destroyed Sunday as she was coming to pick up some basic items for her child.
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A Ukrainian serviceman loads a shell onto a tank at a checkpoint in the southern coastal town of Mar …
"I have a little baby and we are temporarily living in a dormitory. We wanted to get the stroller, some warm clothes for the child," she said, quietly sobbing on a bench across the road from her burning home. "There was no way to get into the house."
Ukraine, Russia, the Kremlin-backed separatists and the Organization for Security and Cooperation in Europe signed the cease-fire deal in the Belarusian capital, Minsk, on Friday evening in an effort to end the bloodshed. The negotiators agreed on the withdrawal of all heavy weaponry, the release of all prisoners and the delivery of humanitarian aid to devastated cities in eastern Ukraine.
The 12-point agreement, published Sunday by the OSCE, also obliges Kiev to give greater powers to the separatist Donetsk and Luhansk regions and calls for local elections to be held in those Russian-speaking regions.
Western leaders voiced skepticism over Russia's commitment to the deal. A previous 10-day cease-fire, which each side repeatedly accused the other of violating, yielded few results at the negotiating table.
German Foreign Minister Frank-Walter Steinmeier said Sunday that the shelling in Donetsk and Mariupol showed the fragility of the cease-fire and described it as only the first step.
"The cease-fire should lead the way for an exchange of prisoners, an effective control of the border and, last but not least, a dialogue about the political participation of the people from eastern Ukraine in Kiev," he said in a statement.
Ukrainian President Petro Poroshenko's office on Saturday said he and Russian President Vladimir Putin had spoken by telephone and discussed steps "for giving the cease-fire a stable character." But, it said, both leaders assessed the cease-fire as having been "fulfilled as a whole."
Echoing similar allegations by the Ukrainian government and NATO, Amnesty International said that it has evidence that Moscow is fueling the conflict through direct support for separatist fighters. In making its case, the group presented satellite images appearing to show Russian weaponry being brought into Ukraine.
"These satellite images, coupled with reports of Russian troops captured inside Ukraine and eyewitness accounts of Russian troops and military vehicles rolling across the border, leave no doubt that this is now an international armed conflict," said Shetty, who is set to visit Kiev and Moscow in the coming days.
Amnesty also said that the Ukrainian government has subjected residential areas to heavy and indiscriminate shelling.
The group said both pro-government and separatist militia groups had abducted and beaten people suspected of aiding their opponents.
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Peter Leonard in Donetsk, Ukraine, Lynn Berry in Moscow, and Kirsten Grieshaber in Berlin, contributed to this report.