Ukraine's army and pro-Russian rebels in the country's east clashed on Friday, killing at least seven civilians and 11 soldiers in the past 24 hours, Ukraine's military spokesman Andrij Lysenko told reporters in a briefing.

"The enemy continues to build up forces in the main areas of the armed conflict," he added.

Intense fighting was reported from eastern Ukraine's Debaltseve, a strategic railway hub that is the point of contention between the Russia-backed rebels and Ukraine's forces. Separatist forces had almost completely encircled a Ukrainian garrison in Debaltseve, compromising the garrison's access to supply routes, the Associated Press said.

The casualties were the first to be reported after leaders of France, Germany, Russia and Ukraine met in Belarus' capital, Minsk, and signed a deal with rebel representatives to enforce a ceasefire that goes into effect at the beginning of Sunday morning (2200 GMT Saturday).

Enforcing a buffer zone

Once the ceasefire is enforced, both sides are expected to withdraw heavy weapons from the frontline and discuss the exchange of prisoners, although there were doubts on whether Russia would release a Ukrainian pilot it had detained.

"It goes without saying the Ukrainian side brought it up, but the president (Russia's Vladimir Putin) repeated his position, that has been voiced many times before, that in this case, she is under investigation and the degree of her guilt or innocence will be established by a court," Russian government spokesman Dmitry Peskov said .

Russia, however, expected all points of the deal to be implemented, Peskov added.

The Kremlin spokesman also said leaders from Russia, Ukraine, Germany and France were in touch over the Ukraine crisis and that Moscow was expecting a phone conversation to be agreed upon in the coming days.

Meanwhile, US and EU leaders maintained pressure on Russia by holding on to their sanctions against Moscow. The leaders believe that Russia backs separatists in Ukraine's east, but Moscow has denied the allegation.

The Organization for Security and Cooperation in Europe is tasked with observing the ceasefire. The group's head, Lamberto Zannier, said in Kyiv that he hoped hostilities would be halted by the Sunday deadline.

"We would really hope to see a decrease already between now and that moment," he said.

The OSCE will have to patrol a 50-km (31-mile) buffer zone to be established between Ukrainian military troops and pro-Russian separatists.

The Ukraine crisis has resulted in the deaths of more than 5,400 people since it began last year in April.

mg/sms (Reuters, AP, AFP)