Ukrainian troops have regained control of the main airport in the eastern city of Donetsk. More than 30 pro-Russian separatists who seized the airport early on Monday, were reported killed.
"The airport is under our full control,'' Interior Minister Arsen Avakov said in a statement on Tuesday. ''The enemy suffered heavy losses. We have none."
He said operations were still continuing. Sporadic gun and artillery fire could be heard into the afternoon.
A coroner told the BBC he had seen 37 bodies, among them two civilians.
Other reports of the death toll vary: Donetsk mayor Alexander Lukyanchenko said 40 people had been killed in the past day, while other rebel leaders said the final toll could rise above 100.
The BBC reports the attempt to seize the airport may have been intended to prevent new President Petro Poroshenko from travelling there after he said his first trip would be to visit the east. He has vowed eastern Ukraine would not be "turned into Somalia".
Meanwhile, the Organization for Security and Co-operation in Europe said it has lost contact with a monitoring team.
The OSCE said four monitors were on a routine mission east of Donetsk when they were stopped at a checkpoint on Monday. They have not been heard from since 6pm that day.
They were Turkish, Swiss, Estonian and Danish.
In April, seven international military observers linked to the OSCE were held captive in eastern Ukraine for a week.