YANGON, Myanmar — Myanmar's government unexpectedly allowed the country's leading opposition figure, Aung San Suu Kyi, to leave house arrest briefly on Sunday and meet with a U.N. envoy trying to persuade the junta to ease its crackdown against a pro-democracy uprising.

But thousands of troops locked down Myanmar's largest cities, and scores of people were arrested overnight, further weakening the flagging movement. And Ibrahim Gambari, the U.N.'s special envoy to Myanmar, failed to see either the junta leader or his deputy in his scheduled meetings. The diplomat was returning late Sunday to the military government's headquarters for a possible third meeting.

The demonstrations seeking to end 45 years of military dictatorship drew international attention after thousands of Buddhist monks joined in. At the height of the protests, some 70,000 people turned out, but were crushed on Wednesday and Thursday when government troops opened fire into the crowds.

The government says 10 people were killed, but independent sources say the number is far higher. A video shot Sunday by a dissident group, Democratic Voice of Burma, showed a monk, covered in bruises, floating face down in a Yangon river. It was not clear how long the body had been in the river.

A U.N. statement said Ibrahim Gambari met Sunday with the acting prime minister, the deputy foreign minister and the ministers of information and culture. While these officials have senior positions in the ruling coterie, the final say in all decisions rests with junta leader, Senior Gen. Than Shwe, and to some extent Deputy Senior Gen. Maung Aye.

Gambari "looks forward to meeting ... Than Shwe," before he leaves the region, a U.N. statement said.

Gambari's efforts began on Saturday when he came from Singapore to Yangon and was immediately flown to Naypyitaw. After his meetings Sunday, he returned to Yangon and was whisked to the State Guest House to meet Suu Kyi, who was brought out of house arrest to see him in what appeared to be an unexpected concession by the junta.

Gambari and Suu Kyi met for over an hour, the U.N. statement said, but gave no details.

"We want Mr. Gambari to stay here long enough to get under way a genuine process of national reconciliation," Britain's ambassador Mark Canning said. "He should be given as much time as that takes. That will require access to senior levels of government as well as a range of political actors."

The U.N. has repeatedly failed to bring about a reconciliation between the military government and the pro-democracy opposition. Gambari and his predecessor, Razali Ismail of Malaysia, have also failed to secure freedom for Suu Kyi, the 1991 Nobel Peace prize winner who has come to symbolize the struggle for democracy in Myanmar.

Her National League for Democracy party won the 1990 general elections, which the junta called after crushing a much larger pro-democracy movement in 1988. But the party was never allowed to take power, and many of its top members were jailed. Suu Kyi has spent 12 of the last 18 years under house arrest.

On Sunday, the number of troops in Yangon, the largest city, swelled to about 20,000 after reinforcements arrived overnight, ensuring that almost all demonstrators would remain off the streets, an Asian diplomat said on condition of anonymity.

"I think the chance of protesters coming to the road and mobilizing enough people to topple the junta is zero," he said.

A few monks were seen in a neighborhood on their customary morning round for alms.

"We are not going to protest any more. Rather we will conduct peaceful protests. We Buddhists believe that dhamma (Buddha's teachings) will finally win over evil," said one monk.

People suspected of leading or organizing the rallies continue to be arrested, the Asian diplomat said, estimating the total number could be as high as 1,000, including several prominent members of the NLD. They joined an estimated 1,100 other political detainees who have languished in jails since before the current turmoil began Aug. 19 with protests against fuel price increases.

With the main prison overcrowded, people are now being detained in university buildings and educational institutes, he said.

Monks and residents spoke on condition of anonymity fearing reprisals.

"We apologize to foreigners for feeling unsafe ... People in this country are very nice and gentle, but the soldiers are very rough," said one resident.

A resident who identified himself as Ko Hla wrote on his Internet blog that troops in downtown Yangon were searching every bag. "If someone got caught with a camera in it, they would arrest him. They arrested anyone that they suspect," he wrote.

The crackdown has triggered unprecedented criticism of Myanmar's generals from almost every corner of the world — even some from China, the country's chief trading partner, which urged the ruling junta to "exercise restraint and use peaceful means to restore its stability as soon as possible."

But China, India and Russia do not seem prepared to go beyond words in dealing with the junta, ruling out sanctions as they jostle for a chance to get at Myanmar's bountiful and largely untapped natural resources, especially its oil and gas.

Pope Benedict XVI joined world leaders in expressing serious concern about the situation in Myanmar. About 1 percent of the country's 54 million people are Catholics. Another 3 percent belong to other Christian denominations.

"I want to express my spiritual closeness to the dear population in this moment of the very painful trial it is going through," he said.

Worshippers at Yangon's Catholic churches read posted bulletins from its hierarchy stating that priests, brothers and nuns were not to become involved in the monthlong protests, but that lay Catholics could act as they saw fit.