In the first Ukrainian military action against the pro-Russian uprising in the east of the country, special forces have recaptured a small airport that had been occupied by militiamen, the government said.
Heavy gunfire rang out at the airport near the town of Kramatorsk. Russian state television reported four to 11 people had been killed, but there was no independent confirmation of any casualties. Much of the shooting appeared to have been warning shots fired into the air.
Ukraine's acting president, Oleksandr Turchynov, had earlier announced an "anti-terrorist operation" against insurgents who have seized control of numerous buildings in the east of the country.
Armed pro-Russian militias are occupying government, police and other administrative buildings in at least nine cities in the Russian-speaking region of the country around the major industrial city of Donetsk. They are demanding broader autonomy and closer ties with Russia.
The central government has so far been unable to rein in the insurgents, and many local security forces have switched over to their side.