A Kachin Independence Army spokesman said the shooting of the aircraft was in response in attacks on their troops by the Myanmar military using jet fighters and helicopter gunships.
The Kachin Independence Army says it shot down a Tatmadaw helicopter gunship on Monday, during fierce clashes near the town of Momauk in southern Kachin State.
The claimed downing of the aircraft comes a day after a renewed junta crackdown on anti-coup protests left at least five civilians dead.
Myanmar has been in turmoil since the military ousted the civilian government and seized power on February 1.
Security forces have sought to quell near-daily pro-democracy protests with deadly force, while long-simmering conflicts with ethnic armed groups have erupted into fierce fighting.
The KIA, which has waged a decades-long insurgency against the military in Kachin and northern Shan states, has been hit in Kachin by air strikes in recent weeks.
“They used jet fighters and helicopter gunships since eight this morning to attack our troops. Our troops fired back and this was how the helicopter was shot down,” said KIA spokesman Colonel Naw Bu, who refused to give details of the weaponry used to down the chopper.
AFP has tried to contact the Myanmar military to seek its account of events, but has not had a response.
Several of Myanmar’s myriad ethnic armed groups have come out in support of the anti-coup protest movement, offering shelter and even training to activists who have fled the crackdown.
The Assistance Association for Political Prisoners, a local monitoring group, said that at least five civilians were killed in operations to break up protests on Sunday.
AAPP said it was the highest single-day death toll since an ASEAN summit on the Myanmar crisis last month.
A total of 765 civilians have been killed in the crackdown, according to the AAPP, though the military disputes the toll, giving a much lower figure.
More than 4,500 people have been arrested, the monitor has said, including dozens of journalists.
On Monday – World Press Freedom Day – a group of foreign embassies in Myanmar condemned the junta’s treatment of journalists, saying they had become a “target of repression”.
Independent media outlets have been shut down or had their licences revoked, and Myanmar authorities have throttled internet access in an apparent effort to stem the flow of information about the protests and crackdown.
“We call for the immediate release of all media workers, the establishment of the freedom of information and communication and for the end of all internet restrictions in Myanmar,” said the statement, noting that of 80 journalists arrested by the authorities, more than half were still detained.
The signatories included the embassies of the United States, the European Union, Australia, Britain, France and Germany.