Officials say four pro-Russian rebels, a Ukrainian soldier, and one civilian were killed in clashes that broke out over the past 24 hours in violation of a February truce deal.
The civilian died during an artillery fire attack on the Avdiyivka coke and chemical plant, located near of the rebels' de facto capital, Donetsk.
Ukrainian military spokesman Andriy Lysenko told reporters that a resulting fire at the plant caused a small ammonia leak. He did not provide further details.
Lysenko said 12 Ukrainian soldiers were also wounded in clashes across the war zone.
The pro-Kyiv governor of the separatist province of Luhansk said a Ukrainian soldier died when his military ambulance came under fire near the Russian border.
Rebel authorities said four of their fighters were killed and another three injured in the past day.
Fighting was particularly heavy in Shyrokyne, near the strategic port city of Mariupol, military officials from both sides said.