Oleksandr Motuzyanyk, a Ukranian military spokesman, said on Thursday that 13 solders have been injured and seven have been killed in clashes with pro-Russian rebels in the past 24 hours.
"Ukrainian army forces suffered the heaviest casualties near Maryinka and Mariupol," Motuzyanyk said in his statement.
The death toll marks the highest daily losses hat the Ukranian army has suffered since mid-July, with at least five Ukranian soldiers killed near the strategic port city of Mariupol.
Pro-Russian seperatist forces assaulted Ukranian army positions in eastern Ukraine, 90 times overnight and used mortars 31 times, banned gun systems 14 times, tank shells five times along with multiple rocket launchers.
The village of Starohnativka was fired on four times by Russian-supported mercenaries. The village of Chermalyk was also hit twice, while the villages of Novohryhorivka, Prokhorivka, Bohdanivka, Lebedynske, Orlovske and Novoselivka Druha were fired on once.
Russian-led militant groups and Ukraine representatives agreed to temporarily abide by the ceasefire agreement signed in February.
More than 6,500 people have been killed in the conflict in eastern Ukraine since April last year, which started after Russia annexed Crimea. Since the ceasefire was agreed in February, many Ukranian soldiers have died.