Ukrainian television said on Friday that up to 20 soldiers were killed in an attack by armed separatists in east Ukraine, but a military source said the death toll was likely lower.

Despite both sides in the ongoing conflict in east Ukraine tentatively agreeing to a cease-fire around the crash zone of Malaysia Airlines flight MH17, fighting is continuing nearby.

The deadly attack on government troops on Friday morning took place less than 20 kilometers south of the crash site, outside the town of Shakhtarsk, which has been the object of sustained battles for several days and remains in rebel hands.

Defense officials said in a statement that an army convoy was struck by mortars during redeployment.

Ukraine security spokesman Vladislav Seleznev said the attack took place before the end of the 24-hour "day of quiet" declared on Thursday in response to a call for a cease-fire from UN Secretary General Ban Ki-moon.

"The militants are behaving in a cowardly and shameless fashion," Seleznev said. "They used the 'day of quiet' to fire on us."

Ukrainian forces have recently focused their strategy on driving a wedge into an area between the largest rebel-held cities, Donetsk and Luhansk. Shakhtarsk lies on one of two highways linking those cities.

The rebels said they had "captured good trophies" and pushed back government forces around the town of Shakhtarsk, where Kiev said a paratrooper unit moving from one base to another had come under mortar and tank fire.

Shakhtarsk is close to the rolling fields where MH17 came down on July 17, killing 298 people, and fighting has raged around it for several days as the Ukrainian army tries to quell the separatist rebellion.

"Our troops were ambushed," Kiev's "anti-terrorist operation" said in a Facebook statement. "Ten Ukrainian servicemen were killed."

In other violence, city authorities said five civilians were killed and nine injured over the past 24 hours in Lugansk, one of the two big rebel strongholds.

AP - Reuters