"We lost five soldiers in fighting over the past 24 hours and four were injured," army spokesman Andriy Lysenko said.
The troops were killed in clashes with pro-Russian rebels to the north and west of the separatist stronghold of Donetsk.
Over 8,000 people have been killed since the rebels took up arms against Ukraine's pro-Western government last year following the ouster of a Russian-backed president in the capital Kiev.
The violence had significantly abated after the two sides agreed to a renewed truce in September that had largely held.