"Unfortunately, there are losses among our troops again," military spokesman Oleksandr Motuzyanyk told journalists.
One soldier was killed in shelling near Novoluganske village, some 50 kilometres (30 miles) from Donetsk, the main stronghold of Russian-backed rebels.
He was the first Ukrainian serviceman killed by shelling in 2018.
During what Kiev said was an "aggravation" of the situation in the conflict zone over the past 24 hours, two other soldiers were killed when their vehicle hit an unidentified explosive device.
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A news agency based in the rebel area said two civilians were wounded in shelling in Donetsk region.
The war in the former Soviet republic broke out in April 2014 and has claimed more than 10,000 lives.
More than 2,750 Ukrainian servicemen have been killed since the beginning of the fighting, according to the President Petro Poroshenko.
Ukrainian media estimates that Kiev lost over 190 troops in 2017.
Ukraine and its Western allies accuse Russia of plotting and backing the insurgency in retaliation for the February 2014 ouster of Kiev's Kremlin-backed regime.
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