Hundreds of armed police and soldiers patrolled the streets of Lhasa and enforced a strict curfew Sunday in a security clampdown on the Tibetan capital following violent protests that drew negative publicity for China ahead of the Beijing Olympics.

Lhasa was quiet but tense two days after Tibetans torched buildings and stoned Chinese residents in the fiercest challenge to Beijing's rule over the region in nearly two decades.

Hong Kong Cable TV reported that about 200 military vehicles, each carrying 40 to 60 armed soldiers, drove into Lhasa on Sunday. Footage showed streets in Lhasa were mostly emptied with only armored and military vehicles patrolling.

Loudspeakers on the streets repeatedly broadcast slogans urging residents to "Discern between enemies and friends, maintain order." Another slogan called on them to "Have a clear stand to oppose violence, maintain stability."

Witnesses and officials confirmed that residents were being ordered to stay off the streets.

"It is fairly quiet this morning. The police are patrolling the streets. The local people have been persuaded not to go out," said a man at the Lhasa city government offices.

A Lhasa resident who refused to give her name said "the police told us not to leave our homes."

The violence Friday erupted just two weeks before China's Olympic celebrations kick off with the start of the torch relay, which will pass through Tibet.

Xinhua reported at least 10 civilians were burned to death Friday. The Dalai Lama's exiled Tibetan government in India said Chinese authorities killed at least 30 Tibetans and possibly as many as 100. The figures could not be independently verified as China restricts foreign media access to Tibet.

China's communist government is hoping Beijing's hosting of the Aug. 8-24 Olympics will boost its popularity at home as well as its image abroad. But the event already has attracted scrutiny of China's human rights record and its pollution problems.

International criticism of the crackdown in Tibet so far has been mild without any threats of an Olympic boycott or other sanctions.

U.S. Secretary of State Condoleezza Rice called on China "to exercise restraint in dealing with the protests," while the State Department issued a travel alert for Americans in the region.

Rice said she was "concerned by reports of a sharply increased police and military presence in and around Lhasa." Her statement called for China to release monks and others jailed for protesting.

International Olympic Committee president Jacques Rogge said he opposed an Olympic boycott over Tibet.

"We believe that the boycott doesn't solve anything," Rogge told reporters on the Caribbean island of St. Kitts. "On the contrary, it is penalizing innocent athletes and it is stopping the organization from something that definitely is worthwhile organizing."

"What is happening in Tibet and Beijing's responses to it will not affect the games very much unless the issue really gets out of control," said Xu Guoqi, a China-born historian at Kalamazoo College in Michigan.

A meeting of the Standing Committee of the Tibet Communist Party, the ruling body in Tibet, said efforts had to be made "to expose and criticize the evil acts done by the hostile forces and expose the ugly feature of the Dalai (Lama) clique."

In a statement on the Tibet Daily Web site, the group urged swift action against Tibet's independence movement. It said the government should "unite all forces that can be united to wage a people's war against anti-splittism and to maintain stability."

On Sunday, the 11th Panchen Lama Gyaincain Norbu condemned the lawless riot in Lhasa, saying the sabotage acts run counter to the Buddhism tenets.

Norbu, Beijing's choice as the reincarnation of the second highest ranking Buddhist figure, said the rioters' acts "not only harmed the interests of the nation and the people, but also violated the aim of Buddhism."

The boy chosen by the Dalai Lama as the Panchen Lama, disappeared along with his family in 1995.

Lhasa is a sprawling city, and the security clampdown seemed to vary in different parts of the city. A worker at one hostel in the city said the staff were not allowed to leave and they were running out of food.

"There are hundreds of soldiers outside and they will not let us go. There is a market next to our hostel and we have been sneaking in to get a few packets of instant noodles," she said, refusing to give her name.

But a clerk at a Lhasa hotel away from the area where the worst violence took place said nearby shops were open and guests were allowed to leave.

Major-General Feng Zhengjie of the People's Liberation Army told reporters in Beijing outside the National People's Congress that the government needs to pay "high attention" to this sort of violent action.

"I hope and believe that the local government will handle this matter. It reminds all of us we need to pay attention to internal and external anti-China forces. Nowadays in society and internationally there are some people who don't want China getting strong," he said

Even as Chinese forces appeared to reassert control in Lhasa, sympathy protests had erupted on Saturday in an important Tibetan town 750 miles away in Gansu Province.

Police fired tear gas to disperse hundreds of Buddhist monks and other Tibetans after they marched from the historic Labrang monastery and smashed windows in the county police headquarters in Xiahe, witnesses said.

On Sunday, Gansu provincial governor Xushou Sheng called the protests "a planned and organized destructive activity" and blamed the "outside Dalai group" for instigating the riots.

The unrest in Tibet began last Monday on the anniversary of a 1959 uprising against Chinese rule of the region. Tibet was effectively independent for decades before communist troops entered in 1950.

The protests by Buddhist monks spiraled to include cries for Tibet's independence and turned violent when police intervened. Pent-up grievances against Chinese rule came to the fore, as Tibetans directed their anger against Chinese and their shops, hotels and other businesses.

The details emerging from witness accounts and government statements suggested Beijing was preparing a methodical campaign -- one that if carefully modulated would minimize bloodshed and avoid wrecking Beijing's grand plans for the Olympics.

Law-enforcement agencies in Lhasa issued a notice offering leniency for demonstrators who surrender before the end of Monday and threatening severe punishment for those who do not.

The calculated mix of threats and inducements underscored the difficulties the communist leadership faces in trying to quell a serious challenge to its 57-year rule in Tibet while saving this year's Summer Olympics.