YANGON, Myanmar (CNN) -- United Nations Secretary-General Ban Ki-moon is to send a special envoy to Myanmar amid reports of several deaths in clashes between security forces and thousands of protesters led by Buddhist monks.

Unconfirmed opposition reports put the death toll at five. "A statement from the main Buddhist organization leading the demonstrations said five monks have been killed," Aye Chan Naing, chief editor of the Democratic Voice of Burma, told CNN from his office in Oslo, Norway.

Myanmar's ruling junta acknowledged that one civilian had been killed and three wounded in the suppression of anti-government protests, The Associated Press reported.

CNN's Dan Rivers, reporting from near the MyanmarThai border, said protests had calmed for the night Wednesday in Yangon, the country's largest city.

Meanwhile, Ban's office called on the regime to cooperate with a U.N. envoy, Ibrahim Gambari, due to be "urgently dispatched" to the troubled southeast Asian country.

"He calls on the senior leadership of the country to cooperate fully with this mission in order to take advantage of the willingness of the United Nations to assist in the process of a national reconciliation through dialogue," said a U.N. statement.

"Noting reports of the use of force and of arrests and beatings, the secretary-general calls again on authorities to exercise utmost restraint toward the peaceful demonstrations taking place, as such action can only undermine the prospects for peace, prosperity and stability in Myanmar."

Speaking from neighboring Thailand, the spokesman for the resistance organization the National Council of the Union of Burma (Myanmar), Soe Aung, told CNN that at least one monk died after clashes with security forces in Yangon.

The AFP news agency also reported officials as saying that at least three monks had died, including one who was shot as he tried to take a firearm from a soldier.

The agency also reported officials as saying that two other monks had been beaten to death. A protester who was not a monk had died after being shot, it quoted Yangon General Hospital as saying.

It is not known if these fatalities are the same as those reported by the Democratic Voice of Burma and the National Council of the Union of Burma.

Witnesses said the violent crackdown came as about 100 monks defied a ban by venturing into a cordoned-off area around the Shwedagon Pagoda.

Mark Canning, the British ambassador to Myanmar, told ITN by phone Wednesday that tear gas was used against monks gathered at the pagoda.

"A number of monks were severely beaten, (and) there have been two or three volleys of shots across the heads of demonstrators," he said.

Authorities ordered the crowd to disperse, but witnesses said the monks sat down and began praying, defying the military government's ban on public assembly.

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Security forces at the pagoda "struck out at demonstrators" and attacked "several hundred other monks and supporters," an opposition Web site detailed.

Authorities ushered away the monks and loaded them into waiting trucks while several hundred onlookers watched, witnesses said. Some managed to escape and headed toward the Sule Pagoda.

Canning also said the country's military regime had ordered a dusk-to-dawn curfew.

"I think the question then was whether all these measures would intimidate people into not marching as they had been for the last eight days, and I think the answer is that it did not," he said.

Canning said about 10,000 people marched Wednesday on the street in front of the British Embassy in Yangon.

"They were a mix of monks and civilians," the diplomat said. "They were entirely peaceful, entirely well-behaved.

"There were several monks, for example, whose feet had to be bandaged because they were walking barefoot, in fact they had been walking barefoot now for over a week and they were bleeding," Canning added.

Opposition reports said that "soldiers with assault rifles have sealed off sacred Buddhist monasteries ... as well as other flashpoints of anti-government protests."

Aye Chan Naing, speaking to CNN, said that any violence used against monks could draw more of the population into the protests. "I think it will really anger the general public," he said. "It's a really shocking situation for a lot of people."

Observers have been preparing for possible violence in Myanmar, where human rights concerns have emerged as an international issue.

"We have no rights, no rights of media, no rights of freedom, no freedom at all," one man told CNN's Rivers.

A small but persistent protest movement against the regime began in August after the government hiked fuel prices.

Since then, authorities have arrested several hundred protesters, but demonstrations led by the monks have gone largely unchallenged by the military, which has ruled the country since the 1960s.

British Prime Minister Gordon Brown Wednesday underscored that any trampling of human rights would not be accepted.

"The whole world is now watching Burma and this illegal and oppressive regime should know that the whole world will hold it to account," he said, speaking at the Labour Party conference. "I want to see all the pressures of the world put on this regime."

Speaking to the U.N. General Assembly's annual session Tuesday, U.S. President George W. Bush said his administration will impose stiffer sanctions against the country's military regime.

"The United States will tighten economic sanctions on the leaders of the regime and their financial backers. We will impose an expanded visa ban on those responsible for the most egregious violations of human rights, as well as their family members," he said.

"We will continue to support the efforts of humanitarian groups working to alleviate suffering in Burma (the country's traditional name) and urge the United Nations and all nations to use their diplomatic and economic leverage to help the Burmese people reclaim their freedom." E-mail to a friend

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