Thirteen soldiers were reportedly killed at a Ukrainian military checkpoint that was attacked by pro-Russian insurgents in a village in the eastern Donetsk region, which separatists declared a “sovereign” republic last week. Witnesses said about 30 Ukrainian troops were also wounded in the attack.

“We do have people killed on our side,” Andriy Parubiy, the head of the Ukrainian National Security Council, told reporters in Kiev. He said Ukrainian security forces were attacked and some were killed in fighting near Volnovakha in Donetsk.

He declined to give a casualty figure but said another battle was ongoing near Rubizhne, a town in the Luhansk region, a second area declared a sovereign republic after a chaotic referendum there on May 11.

Ukrainians are scheduled to go to the polls on Sunday in presidential and mayoral elections that could determine the very make-up of the country and its alignment between Russia and the West. The separatists, who have seized government buildings and clashed with troops, are boycotting the elections.

“There was a huge operation being prepared today in many directions, and every attempt has been repelled,” Parubiy said. At least 60 separatists also commandeered an electric train in Luhansk and attempted to reach the town of Svatove, he said. Ukrainian security forces captured the train and turned it back, he said.

Russia trying to disrupt elections: Acting Ukrainian PM 

Acting Ukrainian Prime Minister Arseniy Yatsenyuk told journalists in Kiev that the interim government is pressing for an urgent UN Security Council session to show that Russia is escalating the conflict and trying to disrupt the elections.

“Provocations by the Russian side in Ukraine are regarded as attempts to disrupt the presidential elections on May 25 and to destabilise the situation in the eastern region of our country,” the Ukrainian Foreign Ministry said in a statement.

The Foreign Ministry said Ukrainian border guards repelled an attack on Wednesday by “several groups of armed militants” who were trying to enter Ukraine from Russia in the Luhansk region.

Describing one of the attacks, the Interior Ministry said in a statement that three trucks and a sport utility vehicle attempted to cross the border at 10.00 pm on Wednesday without stopping at checkpoints. The border guards fired warning shots, and the cars sped back into Russia, it said.

The ministry said that an hour later, a group of people armed with assault rifles, grenade launchers and sniper rifles attempted to storm a separate border post, also in the Luhansk region. Five border guards were injured, the ministry said, and the guards destroyed “two sniper groups.”

The Foreign Ministry also said that a Russian Mi-8 helicopter violated Ukraine’s airspace on Wednesday.

In Kiev, the head of an international effort to foster a national dialogue called for an informal cease-fire ahead of the Sunday elections.

“To the government and also to those who use violent means in the east to oppose the government, I’d appeal to lay down arms at least for the time needed to conduct these elections,” said Wolfgang Ischinger, a German diplomat who has headed three roundtable discussions in Ukraine in the last two weeks.

Neither side has given any indication that it would step back ahead of the voting.

Valeriy Bolotov, head of the self-proclaimed People’s Republic of Luhansk, declared martial law in the territory on Thursday, the Kyiv Post reported. It was unclear what martial law would entail, but Bolotov said it would remain in effect until Ukrainian troops withdrew from the area. Luhansk separatists declared a curfew earlier this month.

Russian troop withdrawing: Russian Defence Ministry

In Moscow, meanwhile, the Defence Ministry issued another statement about Russian troop withdrawals, saying it has sent four trainloads of weapons and 15 transport planes away from the border area with eastern Ukraine.

The Pentagon said on Wednesday that it has seen Russian troop movements along the Ukrainian border but that it was not clear whether they were part of a pullout. Russian President Vladimir Putin told reporters in Shanghai on Wednesday that he had decided to pull his troops back “as an additional step to help create a favorable environment for the upcoming presidential election.”

He called the elections “a positive step” but also said that “it will be very difficult for us to build relations with those who come to power with punitive operations still underway in southeast Ukraine.”

Russia’s conciliatory stance comes as Ukrainian leaders reported progress in a third session of roundtable national unity talks, held on Wednesday in the shipyard city of Mykolaiv.

Although the talks have sometimes appeared like theatre, with grandstanding speeches broadcast on live television, they have given moderate regional representatives a chance to publicly vent their grievances.

A top Russian CEO said on Thursday that sanctions imposed by the West on Moscow are harmful for business in countries that imposed them and in Russia.

“I would encourage politicians to solve political problems . . . first of all through diplomatic measures and not to cause damage to our economies,” Alexey Mordashov, chief executive of the metals firm Severstal, told an economic forum in St. Petersburg.

The United States and the European Union slapped travel bans and asset freezes on members of Putin’s entourage after Russia annexed Ukraine’s autonomous Crimea region in March.

They have warned of more crippling sanctions if Russia tries to grab more Ukrainian land or attempts to derail the elections.

Kunkle reported from Donetsk and Hauslohner from Moscow. Daniela Deane contributed to this report from London.

The Washington Post