BANGKOK — A group of lawyers investigating a violent crackdown in Myanmar in November that left Buddhist monks and villagers with serious burns contends that the police used white phosphorus, a munition normally reserved for warfare, to disperse protesters.

The suppression of a protest outside a controversial copper mine in central Myanmar on Nov. 29 shocked the Burmese public after images of critically injured monks circulated across the country. It also gave rise to fears that the civilian government of President Thein Sein, which came to power in 2011, was using the same repressive methods as the military governments that preceded it.

Burmese lawyers and an American human rights lawyer gathered material at the site of the protest, including a metal canister that protesters said was fired by the police. It was brought to a private laboratory in Bangkok, which found that residue in it contained high levels of phosphorus. Access to the canister and a copy of the laboratory report were provided to a reporter.

“We are confident that they used a munition that contained phosphorus,” said U Thein Than Oo, the head of the legal committee of the Upper Burma Lawyers Network, which helped investigate. “They wanted to warn the entire population not to protest. They wanted to intimidate the people.”