Ukraine in dawn raids on rebels

ROUGH CUT - NO REPORTER NARRATION<br/> <br />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.<br/> <br />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.<br/> <br />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.<br/> <br />Russia denies the charge, describing the separatists as Russian-speakers defending their rights from a possible assault by Kiev's pro-Western leaders.<br/> <br />Pro-Russian separatists in Slaviansk, the eastern Ukrainian where the rebels ar