File Photo: Ukrainian Army troops receive munitions at a field on the outskirts of Izyum, Eastern Ukraine, Tuesday, April 15, 2014. AP
Kiev has been battling a pro-Moscow insurgency in two breakaway regions bordering Russia since 2014, when the Kremlin annexed Ukraine's Crimean peninsula.
Russia has massed troops near Ukraine's borders and the West has for weeks accused it of planning an invasion, warning Moscow of massive sanctions should it launch an attack.
The Ukrainian army said separatists had targeted its positions with grenade launchers and mortars.
"One serviceman was fatally wounded," and another soldier was injured, it said on Facebook.
Kiev and its allies accuse Russia of supporting the rebels militarily -- claims which Moscow denies.
The latest death brings Ukraine's toll in the simmering conflict to 65 since the start of the year, according to an AFP tally based on official figures, compared to a total of 50 in all of 2020.
Russia has massed around 100,000 troops on its side of the border.
US President Joe Biden warned his Russian counterpart President Vladimir Putin of "sanctions like he's never seen" should the troops attack Ukraine.
European Union leaders on Thursday urged Moscow to halt its military build-up and return to talks led by France and Germany.
The conflict in eastern Ukraine has so far left more than 13,000 dead.