Four Ukrainian soldiers were killed in a grenade attack in the war-torn east of the country on Tuesday, Kiev said, the highest daily casualty toll over the past two weeks.
The troops died in a rocket-propelled grenade attack near the village of Pavlopil close to the Kiev-controlled port city of Mariupol, said Oleksandr Danylyuk, secretary of the National Security and Defense Council.
Tuesday's casualties were the highest daily toll since a truce went into force on July 21 - the latest attempt to ease hostilities between Ukraine forces and pro-Russian separatists.
"This crude violation of the truce agreements will not go unnoticed," Danylyuk said on his Facebook page.
In a separate attack, Moscow-backed separatists after midnight fired at the positions of the Ukrainian army near the village of Bogdanivka located south of the Donetsk rebel stronghold, military spokesman Dmytro Gutsulyak said.
Separatists used an infantry fighting vehicle, grenade launchers, and heavy machine guns, he said.
Ukrainian forces and pro-Russian separatists, who carved out two "people's republics" in eastern Donetsk and Lugansk regions, have fought since April 2014, after the annexation of Crimea.
Some 13,000 people have been killed in the violence that Kiev blames on Russian President Vladimir Putin.
Moscow has denied the claims it has funnelled troops and arms across the border despite overwhelming evidence to the contrary.
A series of truce agreements have helped significantly dampen the hostilities although sporadic clashes continue.