Ukrainian government warplanes on Monday bombed the illegal armed groups that had seized Donetsk airport and refused to surrender.

"At 1300 the terrorists who had illegally penetrated onto the territory of the airport in Donetsk were issued an ultimatum for them to lay down their arms and surrender to the counterterrorist operation forces. It has been reported that if the demands were not satisfied the Ukrainian military would take the military option to liberate the airport," Vladyslav Selezniov, spokesman for the anti-terrorist operation, said on Facebook.

He said the ultimatum had been ignored, and so "an air strike was carried out against the terrorists' positions."

First of all, a Sukhoi Su-25 jet delivered warning strikes to force the gunmen to surrender. "Panic began in the militants' ranks. After that, a Mikoyan MiG-29 attacked places where terrorists had built up pockets of resistance." Selezniov said.

Later, he said a strike from a combat helicopter had destroyed a surface-to-air missile system at the airport that was being used by the militants.

He denied reports that the pro-Russian forces had shot down a Ukrainian helicopter.

Meanwhile the self-proclaimed "Donetsk People's Republic" said warplanes were making circles over the airport and that a missile fired by one of them had hit the Tochmash plant, a manufacturer of equipment for geological prospecting and for oil and gas and mining industries.

"Donetsk. One of the missiles has hit the premises of the Tochmash plant. There are two volleys of smoke over the airport. Gunfire can be heard. There are aircraft in the sky," the "Donetsk People's Republic" said on Twitter.