The sound of intensive explosions began at 0600 GMT and appeared to come from the area around Donetsk airport, one of several key flashpoints where shelling has rumbled on despite the February truce deal damping down fighting around much of eastern Ukraine.
The Ukranian army said rebels located near the airport had used small arms, 82mm mortars and rocket-propelled grenades against government troops overnight Saturday, but it did not announce any casualties.
The overall rate of fighting has declined sharply in the weeks since the peace deal hammered out by the leaders of France, Germany, Russia and Ukraine, which obliges both sides to stop shooting and withdraw heavy weapons.
However, sporadic clashes with small arms and mortars has continued on a near daily basis at hotspots including the airport and around the key port of Mariupol.
According to the army, militants fired 120mm mortar shells at the village of Shyrokyne, a village around 20 kilometres east of Mariupol, overnight Saturday.
Under the terms of the ceasefire, the two sides agreed to pull back their heavy arms to create a buffer zone of between 50km and 140km (31 miles and 87 miles), depending on the range of the weaponry.
The warring parties both claim that they have withdrawn their big guns but the Ukrainian military on Friday accused separatists near Shyrokyne of using the heavy Grad multiple rocket system for "the first time in a month".
Moscow on Saturday claimed that Kiev might be "bluffing" over it weapons withdrawal.
Ukraine President Petro Poroshenko, however, insisted late Saturday that Kiev was adhering to the peace deal.
"Firstly, we ceased fire, secondly, we withdrew heavy equipment and artillery, thirdly, we ensured active work of OSCE monitors, who are able to check the implementation of these agreements".
