Separatist rebels have killed at least 13 Ukrainian soldiers in clashes in the east of the country. The violence comes just three days before a crucial presidential poll that the government hopes could calm tensions.
Thursday's attacks were the deadliest for the Ukrainian military since it launched an offensive six weeks ago to quell a pro-Moscow insurgency.
The Ukrainian defense ministry said the worst of the two overnight clashes had seen rebels blow up a military vehicle after firing mortar shells and grenades at a military roadblock near the town of Volnovakha in the Donetsk region.
It said 13 soldiers were killed and more wounded in Volnovakha, while another soldier was killed and two injured in an attack near Rubizhne in Luhansk.
Separatist rebels in Ukraine have so far seized more than a dozen eastern cities and towns in an insurgency that has claimed well over a hundred lives.
Insurgents have declared martial law in the self-proclaimed republic of Luhansk, with a spokesman saying it would remain in place until the Ukrainian government withdraws its troops from the region.
Election in jeopardy
Thursday's violence has overshadowed preparations for Ukraine's presidential vote on Sunday, which the separatists in the east have pledged to derail, intimidating election officials and voters in some regions.
Moscow has so far refrained from recognizing the legitimacy of the separatists' self-declared republics in Luhansk and Donetsk, and Russia's President Vladimir Putin has ordered the withdrawal of some 40,000 troops from Ukraine's borders, though no actual pull-out has been independently confirmed.
However, the interim government in Kyiv still sees Moscow as supporting the insurgency in the east, saying Russia wants to prevent the election from taking place.
On Thursday, it called for a special meeting of the UN Security Council before the election, at which it claimed it would prove Russian intervention.
"At the meeting, we will submit evidence that Russia wants to torpedo the presidential election with an escalation of the conflict," Prime Minister Arseniy Yatsenyuk said in Kyiv.
Separatist unrest has grown in Ukraine since Russia annexed the Ukrainian peninsula of Crimea im March. The move has drawn international condemnation.
tj/hc (dpa, AP, AFP)