Beijing acknowledged that last week's anti-government protests had spread far beyond Tibet's borders and that police opened fire on protesters. It warned foreign tourists and journalists to stay away from a huge expanse of territory across four provinces.
In an overture of peace, the Dalai Lama offered to meet with Chinese President Hu Jintao and other leaders, reiterating that he was not asking for Tibetan independence.
China has repeatedly ignored calls for dialogue, accusing the exiled Tibetan leader and his supporters of organizing violence in hopes of sabotaging the upcoming Beijing Olympics and promoting Tibetan independence.
Hundreds of paramilitary troops aboard at least 80 trucks were seen traveling along the main road winding through the mountains into southeastern Tibet. Others set up camp and patrolled streets in riot gear, helmets and rifles in the town of Tiger Leaping Gorge, a tourist attraction in Yunnan province bordering Tibet.
Farther north, the largely Tibetan town of Zhongdian, renamed Shangri-la a decade ago, was swarmed by 400 armed police. Many carried rifles and what appeared to be tear gas launchers. Residents walked freely among the military, and there was no sign of a daytime curfew.
The troop mobilization was helping authorities reassert control after the broadest, most sustained protests by Tibetans against Chinese rule in decades. Demonstrations had flared across Tibetan areas of Sichuan, Gansu and Qinghai provinces in support of protests that started in the Tibetan capital of Lhasa.
Led by Buddhist monks, protests had begun peacefully in Lhasa early last week but erupted into rioting on March 14, drawing a harsh response from Chinese authorities.
The crackdown drew worldwide attention to China's human rights record, threatening to overshadow Beijing's attempts to project an image of unity and prosperity in the lead-up to the Aug. 8-24 Olympics.
On Thursday, a group of 26 Nobel laureates said they "deplore and condemn the Chinese government's violent crackdown on Tibetan protesters," calling for Beijing to exercise restraint.
"We protest the unwarranted campaign waged by the Chinese government against our fellow Nobel Laureate, his holiness the Dalai Lama," the group said in a statement released by the Elie Wiesel Foundation.
Tibetan exile groups have said 80 people were killed in the protest and its aftermath, while Beijing maintains that 16 died and more than 300 were injured.
Tibetan television in Lhasa showed video Thursday of black-clad police arresting 24 men. Handcuffed against a wall, the men - some young, some old - were charged with "endangering national security, beating, smashing, looting and burning."
China forced the last remaining foreign journalists out of Tibet on Thursday, and stepped up restrictions on Internet and radio reports from people within the country, a media watchdog said.
Georg Blume, a correspondent for German newspapers Die Zeit and taz, and Kristin Kupfer of the German EPD news agency, left after being confronted by an official who threatened to cancel their Chinese visas, Reporters Without Borders said.
Earlier this week, Economist correspondent James Miles and a group of 15 Hong Kong reporters also were forced out.
"If they don't have anything to hide, then why are they making foreign journalists leave? It's clear that they don't want any witnesses," said Vincent Brossel, who heads Reporters Without Borders' Asia desk.
On Thursday morning, an Associated Press photographer was turned away from a flight to Zhongdian in Yunnan province. There were 12 policemen, some with automatic weapons, at the check-in counter. The police said no foreigners were allowed to travel to Tibetan areas due to the protests.
Beijing has warned foreign tourists and journalists to stay away from a huge expanse of territory across four provinces, acknowledging that last week's anti-government protests have spread far beyond Tibet's borders.
Speaking from the seat of his government-in-exile in Dharmsala, India, the Dalai Lama offered to meet with Hu and other Chinese leaders but said he would not travel to Beijing unless there was a "real concrete development."
"The whole world knows the Dalai Lama is not seeking independence, one hundred times, thousand times I have repeated this. It is my mantra - we are not seeking independence," the 72-year-old Dalai Lama told reporters.
"The Tibet problem must be solved between Tibetan people and Chinese people," he said.
The Chinese Foreign Ministry, meanwhile, expressed "grave concern" over a planned meeting between British Prime Minister Gordon Brown and the Dalai Lama, telling Brown not to offer support to the Tibetans' exiled spiritual leader.
Tibet's hard-line Communist Party boss Zhang Qingli this week labeled the Dalai Lama a "wolf in monk's robes" and said Beijing was in a "life-and-death" struggle with his supporters.
China says the riots and protests were organized from abroad by the Dalai Lama and his supporters.
Reinforcing that claim, state broadcaster China Central Television aired a 15-minute program Thursday night, showing how Tibetan rioters rampaged through Lhasa last week but none of the ensuing police crackdown.
Video from security cameras showed burned shops, wounded Chinese and a knife-wielding Tibetan standing atop a police car. Buddhist monks were shown throwing sticks and other debris at riot police in a scuffle on March 10, in an attempt to portray the protests as having been started by monks.
But authorities have moved to clamp down on unrest in Tibet and surrounding provinces, where more than half of China's 5.4 million Tibetans live. Moving from town to town, police have set up blockades and checkpoints to keep Tibetans in and reporters out.
Foreign Ministry spokesman Qin Gang said China is "suggesting" foreigners stay out of Gansu and Sichuan provinces for safety reasons.
But tour operators in the provinces said foreigners were barred from traveling in those areas and tour groups were banned from Tibet, isolating a region about four times the size of France.
An employee at the Nine Lakes Travel Agency in Lanzhou, Gansu province, said she had heard about recent protests and unrest in many counties around the province.
"Tourists are not allowed to enter the seven counties affected because it considered dangerous at the moment. It is not safe to travel here at this time," she said, refusing to give her name for fear of reprisal.
Despite the massive security, protests have continued to crop up in towns in Qinghai, Sichuan and Gansu provinces.
The official Xinhua News Agency said police shot and wounded four rioters "in self-defense" during violent protests Sunday in Aba County in Sichuan. It is the first time the government has acknowledged shooting any protesters during the unrest.
A Tibetan resident in Aba County said Thursday she had heard of numerous arrests of protesters.
"There are many, many troops outside. I'm afraid to leave the house," said the woman, who refused to give her name for fear of retaliation by authorities. Police could be heard shouting from loudspeakers for protesters to turn themselves in.
Troops blocked roads in nearby Sertar, also in Sichuan, confining residents to their homes, said a woman reached there by phone. The London-based Free Tibet Campaign reported that troops had been sent to the county after residents blew up a bridge near the village of Gudu.
A hotel worker in central Luqu County, in neighboring Gansu province, said she had not left the hotel in four days because she was afraid.
"On the 16th, hundreds of Tibetan protesters marched in the streets, throwing rocks and breaking windows. The streets are now filled with police officers," she said, refusing to give her name for fear of reprisal. "Our hotel is booked out with tourists, but no one feels safe enough to set foot outside."
Adding to Beijing's worries, activists said Thursday they would demonstrate in Beijing during the Olympics to press China to help end bloodshed in Sudan's Darfur region.