Ukraine in dawn raids on rebels

ROUGH CUT - NO REPORTER NARRATION

Ukrainian troops launched a dawn raid to try to retake the rebel stronghold of Slaviansk on Friday, surrounding the eastern town and sending in military helicopters, one of which was shot down by pro-Russian rebels, killing its pilot.

Accusing the pro-Moscow separatists of using mercenaries, Interior Minister Arsen Avakov said the offensive was answered with heavy artillery, with the rebels using grenade and portable anti-aircraft missile launchers to bring down the plane.

Kiev has accused Moscow of financing and arming the separatists, who have seized buildings across Ukraine's eastern Donbass coal and steel belt and demand a referendum on independence on May 11 for at least two eastern regions.

Russia denies the charge, describing the separatists as Russian-speakers defending their rights from a possible assault by Kiev's pro-Western leaders.

Pro-Russian separatists in Slaviansk, the eastern Ukrainian where the rebels ar