Activists say 50 were injured when police attacked them at a copper mine earlier this week.
MONYWA, Myanmar - Buddhist monks marched in Myanmar's two biggest cities on Saturday to protest police violence during a crackdown on demonstrators at a copper mine, while Nobel Peace laureate Aung San Suu Kyi and a rights group called for an official inquiry.
Activists said at least 50 people had been injured Thursday, including more than 20 monks who had ended up in hospital, after riot police raided camps set up round the Monywa copper mine by villagers protesting against their forced eviction to make way for an expansion of the project.
Police used tear gas, water cannon and, according to activists, incendiary devices that local media described as "phosphorous bombs". Many of the injured suffered serious burns.
Phil Robertson, deputy Asia director at U.S.-based Human Rights Watch, called for a speedy, impartial investigation by the government.
"A hospital ward full of horribly burned Buddhist monks and other protesters deserve to know who attacked them while they were sleeping and what the government is going to do about it," he said.
"The crackdown ... is a fundamental test case for the government's commitment to peaceful assembly and willingness to demand accountability for abuses," he added.
Myanmar was ruled by a military junta for almost half a century until March 2011, but since then a quasi-civilian government under President Thein Sein has pushed through a series of political and economic reforms, leading Western states to ease sanctions.
Suu Kyi, who led the fight for democracy under the junta and is now a member of parliament, went to the Monywa area in the northwestern region of Sagaing to speak to locals on the day of the police raid. On Friday she also called for an inquiry.
"I think the people have the right to know why such violent measures were taken," she told a news conference. "I think it is needed to apologies to the monks."
She said she had called on the authorities to release any monks who had been detained, but had been told there were no arrests.
A police officer in Monywa, who declined to be named, said arrangements were being made for a formal apology but he declined to give further details.
Around 40 monks accompanied by about 60 other people staged a peaceful march around the Sule Pagoda in the commercial capital, Yangon, a focal point for monk-led protests in 2007 that were brutally put down by the junta.
They walked past the offices of the military-owned Union of Myanmar Economic Holdings Ltd, a partner in the copper mine project with a unit of China North Industries Corp, a Chinese weapons manufacturer.
At the same time, at least 100 monks demonstrated in the second city, Mandalay.
Rallies have been held at the Monywa copper mine, Myanmar's biggest, for more than three months and have been seen as a test both of the new regime's willingness to allow peaceful protest and its attitude to land grabs.
Local residents say the $1 billion mine expansion entails the unlawful confiscation of more than 7,800 acres of land. They told Reuters in September that four of 26 villages at the project site had already been displaced, along with monasteries and schools.
State television said just before the crackdown that all project work had been halted since November 18 as a result of the protests.
Additional reporting by Aung Hla Tun in Yangon; Writing by Alan Raybould