Pro-Russia insurgents have attacked a military checkpoint in eastern Ukraine, reportedly killing at least 13 troops and wounding more than 30.
The attack, near the town of Volnovakha, comes three days before a key presidential vote and is the deadliest so far in weeks of fighting.
A rebel group who claimed responsibility for it said one of their own was also killed.
Local residents said the attackers were hidden inside an armoured bank truck. The unsuspecting Ukrainian soldiers are said to have waved it through and were then shot at point-blank range.
Acting president Oleksandr Turchynov said the rebels fired automatic weapons and rocket-propelled grenades.
Debris was scattered over a wide area According to the Ukrainian Defence Ministry, the ammunition section of one military vehicle was hit and exploded into a fireball.
The turrets were blown off three armoured infantry vehicles which were also burnt along with several trucks.
AP journalists said they saw the bodies of 11 Ukrainian soldiers in a field near the village of Blahodatne, outside Volnovakha, which lies 20 miles south of Donetsk.
Witnesses including a medical worker said more than 30 Ukrainian troops were wounded in the attack, some of them badly.
All the wounded were being treated at nearby medical facilities.
Acting Prime Minister Arseniy Yatsenyuk blamed Russia for backing the rebels in the Donetsk and Luhansk regions, which have declared independence from the government in Kiev. He called for an urgent session of the UN Security Council.
Pro-Russia militants at a Victory Day rally in Donetsk The attack has cast a shadow over Ukraine's presidential vote on Sunday, which separatists in the east have pledged to derail.
Authorities in Kiev see the vote as a chance to defuse tensions and stabilise the country, although they admit it will be impossible to hold the poll in some eastern areas.
In the town of Horlivka, a masked rebel commander claimed responsibility for the raid and showed off a hoard of seized Ukrainian weapons including automatic and sniper rifles and rocket grenade launchers.
"We destroyed a checkpoint of the fascist Ukrainian army deployed on the land the Donetsk Republic," said the commander, who wore a balaclava and identified himself by his nom de guerre, "Bes," which is Russian for "demon."
He said one of his men also was killed in the attack.
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