Ukrainian troops had to open fire at Donetsk airport because the attacks by militants had sharply increased and militants had banned the evacuation of Ukrainian military and the dead from the airport, Ukrainian President Petro Poroshenko said.

"The intensity of the attacks on the Donetsk airport by the terrorists and the unpunished ceasefire violations sharply increased in the past few days. The day before yesterday, I ordered a one-time response because they had just banned us from taking our wounded and dead from the Donetsk airport," he said during a meeting with Polish Prime Minister Ewa Kopacz in Kyiv on Monday.

The president recalled that a document against the use of artillery shelling in Donbas was signed on December 9, 2014.

"This document was effective, but it lasted less than a month because the tensions were escalated considerably after January 7 by Russia and the terrorist groups in the eastern regions," Poroshenko said.

Poroshenko said the number of attacks by the militia on the Ukrainian troops has increased from ten to 90-100 attacks a day.

"These attacks mainly hurt civilians," the president said, recalling the tragedy near Volnovakha on January 13, in which 13 civilians, including children, were killed.

"The Ukrainian Foreign Ministry yesterday issued a statement on my orders saying that we are ready to sign a ceasefire agreement immediately on condition of full observance of the Mink agreements," Poroshenko said.