"Over the past 24 hours, as a result of hostilities one Ukrainian soldier was killed and another three were wounded," military spokesman Andriy Lysenko told reporters.
Lysenko said fighting along the front "has escalated", accusing the insurgents of violating a shaky truce 81 times since Thursday -- the highest number recorded since the end of August.
The soldier died during a mortar attack on the contested village of Zaitseve, a recent flashpoint located 55 kilometers (35 miles) northeast of the rebels' de facto capital Donetsk, AFP reported.
Meanwhile, separatist authorities accused Kiev's forces of also intensifying their attacks in breach of the latest ceasefire agreed on January 13.
More than 9,000 people have been killed and 20,000 injured since the revolt against Ukraine's new pro-Western leadership erupted in April 2014, according to the United Nations.
Kiev and the West accuse Russia of supporting the insurgents and sending regular troops across the border, claims that Moscow denies.