Ukrainian and pro-Russian forces are heading for a showdown in Donetsk, where the armed rebels have called on the local population to evacuate the city, a sign that a full-scale battle may be imminent.

Rebel sources say 50 of their fighters were killed in intense fighting on Tuesday, while Kyiv says 100 terrorists were killed. There are reports that two local police commanders who refused to obey the pro-Russian separatists’ orders were taken from their police station and shot in the head in the street.

“You can see the dead who fell in the fighting for Donetsk airport, all of them from forces of the so-called People’s Republic of Donetsk (PRD). The body count is going to be difficult as casualty figures differ between the two sides,” said the head of the euronews bureau in Kyiv, Sergio Cantone.

There is a mounting sense of impending disaster as the PRD leadership struggles to maintain discipline among its fighters, and commandeers public buildings to use as shelters or makeshift medical centres.

Ukraine’s new President, Petro Poroshenko, has rejected holding any talks with ‘terrorists’, and said that anyone who does not put down their weapon will be killed.

Material damage included the overnight burning of the Druzhba Arena hockey stadium, owned by local Party of Regions member and former minister Boris Koleznikov. He condemned the attack and held the leader of the PRD responsible. He compared the separatists to “Somali pirates”.

NATO said it had seen movement on the border with Russia suggesting a “slow withdrawal” of military forces had begun, and the OSCE said it has lost contact with a group of four observers in Donetsk.