A Tibetan refugee boy plays with a Tibetan flag as his parents and other adults pray outside the Baudhanath Stupa in Katmandu, Nepal, on Saturday during a protest against the Chinese rule in Tibet.

Beijing ? Soldiers on foot and in armored carriers swarmed Tibet’s capital Saturday, enforcing a strict curfew a day after protesters burned shops and cars to vent their anger against Chinese rule. In another western city, police clashed with hundreds of Buddhist monks leading a sympathy demonstration.

Secretary of State Condoleezza Rice called on China “to exercise restraint in dealing with these protests,” while the State Department issued a travel alert for Americans in the region. Her statement also called for China to release monks and others jailed for protesting.

The violence erupted just two weeks before China’s Summer Olympic celebrations kick off with the start of the torch relay, which passes through Tibet. China is gambling that its crackdown will not draw an international outcry over human rights violations that could lead to boycotts of the Olympics.

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

Initially, the protests were led by Buddhist monks demanding the release of other detained monks. Their demands spiraled to include cries for Tibet’s independence and turned violent Friday when police tried to stop a group of protesting monks. Pent-up grievances against Chinese rule came to the fore, as Tibetans directed their anger against Chinese and their shops, hotels and other businesses.

It was the fiercest challenge to Beijing’s authority in nearly two decades.

China’s official Xinhua News Agency reported at least 10 civilians were burned to death on 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.

In the Tibetan capital of Lhasa on Saturday, police manned checkpoints and armored personnel carriers rattled on mostly empty streets as people stayed indoors under a curfew, witnesses said. The show of force imposed a tense quiet.

Several witnesses reported hearing occasional bursts of gunfire. One Westerner who went to a rooftop in Lhasa’s old city said he saw troops with automatic rifles moving through the streets firing, though he did not see anyone shot.

Foreign tourists in Lhasa were told to leave, a hotel manager and travel guide said, with the guide adding that some were turned back at the airport.

“There are military blockades blocking off whole portions of the city, and the entire city is basically closed down,” said a 23-year-old Canadian student who arrived in Lhasa on Saturday and who was making plans to leave. “All the restaurants are closed, all the hotels are closed.”

Even as Chinese forces appeared to reassert control in Lhasa, a second day of sympathy protests erupted in an important Tibetan town 750 miles away.

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.

Also Saturday, fresh demonstrations by Tibetan exiles and their supporters sprouted up in neighboring Nepal as well as New York, Switzerland and Australia.

The Chinese government is hoping a successful Olympics will boost its popularity at home as well as its image abroad.

But Beijing’s hosting of the Olympics has already attracted scrutiny of China’s human rights record and its pollution problems.

So far, international criticism of the crackdown in Tibet has been mild.

The U.S. and European Union called for Chinese restraint without any threats of an Olympic boycott or other sanctions.