KIEV (REUTERS) - Six Ukrainian soldiers have been killed in attacks by separatists in the past 24 hours, the Kiev military said on Friday as fighting raged at the international airport in the big eastern city of Donetsk.

"Six of our servicemen have been killed as a result of combat activity and another 18 have been wounded in the past 24 hours," military spokesman Andriy Lysenko told journalists.

A presidential adviser, Yuri Biryukov, said separatists had launched a full-scale attack on the airport at Donetsk to try to dislodge government forces who have tenuous control on the complex.

"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.