KIEV (Reuters) - Six Ukrainian servicemen have been killed and 14 wounded in separatist eastern territory in the past 24 hours, despite a four-month-old ceasefire deal, the Ukrainian military said on Saturday.

The truce brokered by the leaders of Ukraine, Russia, Germany and France has stemmed large-scale fighting but skirmishes claim lives almost daily on both sides, and international monitors have warned of the threat of a bigger flare-up.

The situation is particularly tense around the airport near rebel-controlled Donetsk city, military spokesman Andriy Lysenko said.

"The enemy threw tanks, armored personnel carriers and heavy artillery into battle. We emphasize that rebels are also firing at residential areas," he said in a briefing.

The casualties were a result of shelling by pro-Russian separatists as well as encounters with mines, he said.

Meanwhile separatist officials accused Ukrainian forces of firing at the village of Oktyabrsky near Donetsk, wounding two civilians, and shelling three districts of the city over the past day, rebel press service DAN reported.

On Thursday, the Organization for Security and Cooperation in Europe said that despite assertions to the contrary, neither side has completed the withdrawal of heavy weapons as agreed in the ceasefire deal.

(Reporting by Alessandra Prentice and Pavel Polityuk; Editing by Raissa Kasolowsky)