Myanmar has charged a group of activists who protested against a controversial Chinese-backed copper mine with defaming the state, police said Tuesday.

The eight demonstrators were picked up a day after they joined a gathering of about 50 people in central Yangon calling for a halt to the Monywa project and urging Chinese joint owner Wanbao to quit Myanmar.

"A protest march is fine but their anti-government slogans were too much," said a police officer who did not want to be named.

The suspects were taken to Yangon's Insein Prison pending a trial scheduled for December 3.

The Monywa copper mine, a joint venture in the northern district of Sagaing between military-owned Myanmar Economic Holdings and Wanbao, has been the subject of controversy for months after local media alleged corruption over the project.

President Thein Sein's government earlier this year approved a bill allowing peaceful protests as part of the political changes sweeping the former army-ruled country. Demonstrators must obtain permission in advance.

Last year Myanmar ordered a halt to construction of a controversial $3.6 billion mega dam in a rare recognition of public opposition to the Chinese-backed hydropower project.