KIEV, Ukraine--Scant progress was made at the first high-level talks in months between Ukraine and pro-Russian rebels in the Belarus capital of Minsk, although both sides said that after hours of talks they did agree to exchange some prisoners.

The combatants said they hope to meet again in Minsk in the coming days to discuss broader measures to end fighting in eastern Ukraine that has killed at least 4,700 this year--more than 1,300 of them since a putative cease-fire in September, according to a United Nations report.

The crucial goals of the talks have been to cement a lasting cease-fire by agreeing on a withdrawal of heavy weaponry from the fighting zone and a demarcation line between rebels and government troops.

On Thursday, officials declined to say what, if any, progress was made on those points in the late-night talks on Wednesday. "The meeting took a fairly long time and the atmosphere was tense," said Denis Pushilin, an envoy to the talks from the rebels" self-proclaimed Donetsk People's Republic. "It was a preparatory meeting and only after the next meeting we would be able to talk about the results."

Ukraine military spokesman Col. Andriy Lysenko said negotiations are ongoing and that "they're not being made public because there are no specific results just yet."

Ukrainian State Security Service said that a swap of prisoners may commence in a matter of days, although a spokeswoman for the agency said "we hope that the deal won't fall apart." The two sides will exchange several hundred prisoners, said Alexander Zakharchenko, the leader of the Donetsk People's Republic, according to a report from the Russian news agency Interfax.

While a swap does mark some progress, officials said both sides would still be holding hundreds more prisoners, and a spokeswoman for the Ukraine Security Service repeated that it favored an "all-for-all" exchange.

The two sides said they had not agreed on a date for the next meeting, but hoped it would be soon. Though the truce announced in September has largely been a failure, an agreed-upon "day of silence" on Dec. 9 helped to reduce fighting, even though Kiev reported sporadic artillery fire.

The daily toll of casualties has trickled off recently, Mr. Lysenko said at a briefing Thursday, with just one Ukrainian serviceman wounded in the last 24 hours.

Meanwhile, friction persists between Kiev and Moscow over the Crimean peninsula annexed by Russia in March. The peninsula, which relies on electricity from Ukraine, suffered a blackout for several hours Wednesday, after Ukraine shut down power from the mainland.

Ukraine's energy minister said Ukraine's electricity grid has suffered a deficit in recent weeks, and halted supplies to Crimea because it was using more than agreed upon. Power delivery was back to normal in a few hours, he said.

Crimean authorities plan to charge Ukraine for the losses caused by the "surprise blackout," according to a report from Russia's Interfax news service.

Nonna Fomenko in Moscow contributed to this article.

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