AFP

The civilian death toll in the Myanmar military's crackdown on protesters passed 520 as armed rebel groups on Tuesday threatened the junta with retaliation if the bloodshed does not stop.

World powers have ramped up their condemnation of the military's campaign against the anti-coup movement that is demanding the restoration of the elected government and the release of civilian leader Aung San Suu Kyi.

Washington suspended a trade pact with Myanmar and UN chief Antonio Guterres called for a united global front to pressure the junta after more than 100 protesters were killed in a bloody weekend.

Adding to that pressure campaign, a trio of ethnic rebel groups on Tuesday condemned the crackdown and threatened to fight alongside protesters unless the military reined in its violence.

Daily rallies across Myanmar by unarmed demonstrators have been met with tear gas, rubber bullets and live rounds.

The Assistance Association for Political Prisoners (AAPP) said it had confirmed a total of 521 civilian deaths by late Tuesday night but warned the true toll was probably significantly higher.

On Tuesday, protesters in Yangon emptied rubbish bags in the streets as part of the latest action.

Eight people were killed Tuesday including a 35-year-old protester in the town of Muse in Shan state, and there were also fatalities at Myitkyina in Kachin state as well as Mandalay and Bago, AAPP said.

State media also reported a protester's death in South Dagon, Yangon, while authorities are investigating a bomb explosion at a police station in the city of Bago which injured a few officers.

Air strikes launched by the junta also killed six people in eastern Karen state, according to the Karen National Union (KNU), one of the country's largest armed groups.