The rebel fighter said the bodies arrived on a truck which was parked outside the hospital and waiting to be checked for explosives by security guards.

There were fierce battles between Ukraine government forces and pro-Russian separatists on Monday.

Rebels have seized government offices and been fighting government troops in the east of the country for more than a month.

Plumes of black smoke could be seen rising from Donetsk's Sergei Prokofiev International Airport after Ukraine fighter jets and helicopter gunships unleashed air strikes on rebels who took control of an airport terminal.

Many flights have been delayed or cancelled and routes to the airport have been blocked by police.

Members of the public were urged to stay indoors following reports the fighting had spread to residential areas of the city.

The government assault, considered the most forceful action so far taken by Kiev against pro-Russian rebels, came just hours after Ukrainian billionaire Petro Poroshenko claimed victory in the country's presidential elections.

His government said the military fired warning shots over the airport after an ultimatum for the insurgents to leave expired.

It then deployed Mi-8 helicopters filled with troops, along with SU-25 fighter jets and MiG-29s to strike the terminal and the runway as rebel fighters shot back from the ground. 

Mr Poroshenko, who described the separatists as 'Somali pirates,' has promised to negotiate a peaceful end to the pro-Russian insurgency in the east.

"The anti-terrorist operation cannot and should not last two or three months," he said. "It should and will last hours."