AFP

Three of the country's myriad armed ethnic insurgent groups known as the Brotherhood Alliance -- the Ta'ang National Liberation Army, the Myanmar Nationalities Democratic Alliance Army and the Arakan Army (AA) -- issued a joint statement threatening retaliation.

"If they do not stop, and continue to kill the people, we will cooperate with the protesters and fight back," the statement said.

If such groups take up arms, the International Federation for Human Rights (FIDH) warned that the situation could degenerate into civil war.

Two dozen ethnic minority rebellions have flared in Myanmar since independence from British colonial rule in 1948, fighting over autonomy, identity, drugs and natural resources.

The military has sought to cut deals with some armed groups and earlier this month took the AA off the list of terrorist organisations.