Ukraine's Defense Minister has accused Russia of launching a "great war" that could claim tens of thousands of lives, BBC News reports.

Russia dismissed the comments, saying they only pulled the Ukrainian people further into a bloody civil conflict. The comments came after Ukrainian troops were forced to flee Luhansk airport in the east of the country amid an offensive by pro-Russian armed groups.

"A great war has arrived at our doorstep - the likes of which Europe has not seen since World War Two," Ukrainian Defense Minister Valeriy Heletey wrote on Facebook on Monday, Sept 1.

"Unfortunately, the losses in such a war will be measured not in the hundreds but thousands and tens of thousands," he added.

Russia has repeatedly denied Ukrainian and Western accusations that it is providing troops and equipment to the militias battling the government forces.

Russia's Foreign Ministry said it was "hard to believe that such statements can be made by the defence minister of a civilized state".

Meanwhile, UN Secretary General Ban Ki-moon said on Tuesday that there could be "no military solution" to the crisis in Ukraine.

The situation was "very chaotic and dangerous" and required "a political dialogue for a political solution" that was sustainable, he told journalists during a visit to New Zealand.

On Monday, Ukraine's army said it had been forced to withdraw from Luhansk airport after it was attacked by Russian tanks.

Ukrainian President Petro Poroshenko said the incident was "direct, overt aggression against Ukraine from the neighboring state".

The latest round of crisis talks got underway in Belarus on Monday but after several hours of negotiations, they were adjourned until Friday.

At least 2,593 people killed in Ukraine since mid-April (not including 298 passengers and crew of Malaysian Airlines MH17, shot down in the area).