An ethnic rebel group in Myanmar said it had shot down a military helicopter on Monday as fighting in the country"s northern and eastern frontier regions intensified following an army coup. Domestic media also reported that a junta-appointed local administrator had been stabbed to death in the main city, Yangon. Violence has spiralled since the Feb. 1 coup, with at least 766 civilians reported killed by security forces and increasing confrontation with ethnic armies on Myanmar"s fringes and junta opponents in the cities and countryside. The United Nations estimates that tens of thousands of civilians have fled their homes to escape fighting between the military and insurgents based along the border. The Kachin Independence Army said the helicopter was shot down around 10:20 a.m. at a village near the town of Moemauk in Kachin province following days of air raids. "The military council launched air strikes in that area since around 8 or 9 this morning ... using jet fighters and also fired shots using a helicopter so we shot back at them," said spokesman Naw Bu by telephone. He declined to say what weapons were used. ​ News portals MizzimaDaily and Kachinwaves also reported the downing of the helicopter next to photographs showing a plume of smoke coming from the ground. A resident in the area, who declined to be named, said by telephone that four people had died in hospital after artillery shells hit a monastery in the village. Reuters could not independently verify the reports and a military spokesman did not answer a phone call seeking comment. Myanmar has been in turmoil since the coup overthrew elected leader Aung San Suu Kyi, with protests almost daily against military rule across the country. In another sign of the growing insecurity, the junta-appointed head of the ward administration office in Yangon"s Tharketa district was stabbed at his office and later died of his wounds, Khit Thit Media said. Two residents of the district confirmed the report. Police did not respond to a request for comment. The Assistance Association for Political Prisoners advocacy group says security forces have killed at least 765 civilians since the coup. The junta disputes the figure and says at least 24 members of security forces have been killed during the protests. The military said it had to seize power because its complaints of fraud in a November election won by Suu Kyi"s party were not addressed by an election commission that deemed the vote fair. Suu Kyi, 75, has been detained since the coup along with many other members of her party.