YANGON, May 3 (Reuters) - The Kachin Independence Army (KIA), one of Myanmar's most powerful rebel groups, said on Monday it had shot down a helicopter after returning fire following air strikes by the military, an official at the group said.

The United Nations estimates that tens of thousands of civilians have fled their homes as a result of the fighting between the military and ethnic minority insurgents in remote northern and eastern frontier regions. The conflict intensified after Myanmar's generals seized power on Feb.1, ousting the elected government led by Aung San Suu Kyi.

The KIA's information department head, Naw Bu, said the helicopter was shot down around 10:20 a.m. at a village near the town of Moemauk in Kachin province.

"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," he said 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, with protests almost daily against military rule across the country.

On Sunday, Myanmar security forces opened fire on some of the biggest protests in days, killing eight people, media reported.

The protests, after a spell of dwindling crowds and what appeared to be more restraint by the security forces, were coordinated with demonstrations in Myanmar communities around the world to mark what organisers called "the global Myanmar spring revolution".

The Assistance Association for Political Prisoners advocacy group says security forces have killed at least 765 protesters since the coup. Reuters is unable to confirm the toll.

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.