File Photo: Ukrainian soldiers strengthen their front line position in the town of Novoluhanske in the Donetsk region, Ukraine, on Dec. 9, 2019. AFP
Tensions around Ukraine have escalated in recent months, as Washington and Kyiv's European allies accuse Russia of threatening the former Soviet country with invasion.
Ukraine said that separatists had targeted its military positions in the east of the country on Tuesday with heavy machine guns and small arms.
"One serviceman of the Joint Forces was fatally wounded," the army said in a statement on Wednesday, adding that its troops had returned fire.
Moscow is accused of massing some 100,000 troops at the Ukrainian border.
The Kremlin describes its troop presence as protection against an encroaching West, particularly NATO, and has demanded wide-ranging concessions from Washington and its allies.
An initial round of US-Russia talks in Geneva on Monday aimed at calming tensions on the Ukraine border proved inconclusive.
The next round of talks begins on Wednesday at NATO's headquarters in Brussels.
Kyiv has been battling a pro-Moscow insurgency in two breakaway regions bordering Russia since 2014, when the Kremlin annexed Ukraine's Crimean peninsula.
The conflict has so far left more than 13,000 dead.