Kiev officials said six Ukrainian soldiers were killed overnight and 18 wounded in attacks by separatists. A seventh soldier was killed on Friday near the airport, an official of the army general staff said.

Government troops have a tenuous grip on the airport, even though the complex, which includes a multi-story control tower and extensive outbuildings, is now only a battered shell after nine months of conflict.

Its cratered runways mean it has not functioned for months as an airport. But it has symbolic value for both sides and has become the main flashpoint in the fighting even as prospects for a new round of peace talks dimmed.

Representatives from Ukraine and Russia, separatist leaders and officials from the Organization for Security and Cooperation in Europe had been tentatively due to meet in the Belarussian capital, Minsk, on Friday to try to get a peace effort and ceasefire back on track.

But the meeting of the so-called 'contact group' did not get off the ground, despite calls from Ukrainian President Petro Poroshenko and German Chancellor Angela Merkel. One rebel official, Denis Pushilin, left Minsk saying he did not know when a further attempt to hold talks would be scheduled.

In a report highlighting the collapse of health care in Ukraine's eastern regions, the Geneva-based World Health Organization on Friday put the death toll from the nine-month conflict at more than 4,800.

"HOT COMBAT"

A presidential adviser, Yuri Biryukov, said separatists had launched a full-scale attack on the airport to try to dislodge government forces.

"They (the separatists) launched a full storm from this morning. We have wounded on our side. There is hot combat going on there and the tension and the situation there is the worst I have seen," Biryukov wrote on his Facebook page.

As night fell, the Kiev military said fighting was still going on and the military situation was constantly changing.

Ukraine, Russia and separatist leaders agreed in Minsk last September on a 12-point peace blueprint for scaling down the conflict, including through a ceasefire.

But the accord was flouted from the start, with each side blaming the other. Kiev says 200 soldiers have been killed since the truce theoretically came into force in early September.

Kiev accuses Russia of failing to comply with the agreement to withdraw Russian fighters and military equipment from the east. Despite what the West and Kiev say is incontrovertible evidence, Moscow denies its troops are involved in the conflict.

Ukraine's parliament voted on Thursday to rotate Ukrainian front-line troops and resume partial conscription after a security official said Russian forces had sharply increased military activity in the east.

Russia reacted to this on Friday saying the move could undermine peace efforts. "Any action related to military preparations does not help the process," Foreign Minister Sergei Lavrov told a news conference.

"We will hope that all this... does not lead to a renewed military confrontation."

(Additional reporting by Pavel Polityuk in Kiev and Gabriela Baczynska in Moscow; Writing By Richard Balmforth; Editing by Crispian Balmer)