Ukraine’s acting president said its forces had retaken control of the Karamatorsk airfield in the east of the country Tuesday as the crisis in the region escalated.
Heavy gunfire was heard in the area but reports of casualties could not immediately be confirmed.
A BBC reporter said that an angry crowd of about 200 local people, including pro-Russian separatists, gathered at the air base after Ukrainian helicopters and fighter aircraft arrived to enforce control of the facility.
Members of the crowd shouted “go home” at Ukrainian military personnel, the BBC said, adding that it was not entirely clear when - or even if - the airfield had been under the control of separatists.
In a statement from his office,acting president Oleksander Turchinov said the action was the first part of an "anti-terrorist operation" against the separatists who have seized control of numerous buildings in the east of the country.
Kramatorsk is just south of the city of Slovyansk, 100 miles, from the Russian border, which has come under the increasing control of separatist gunmen.
Earlier Tuesday, NBC News saw Ukrainian military forces were massing on the outskirts of Slovyansk fortifying positions as fears grew that violent clashes with pro-Russian separatists could escalate.