The 19-year-old Tibetan Buddhist monk, identified as Lobsang Gyatso, set himself ablaze on Monday in Sichuan province's restive Aba county, the International Campaign for Tibet (ICT) and Free Tibet said.

The Washington-based ICT said police violently beat the monk as they extinguished the flames, before taking him into custody. It was not immediately clear whether he survived.

He was a monk at Aba's Kirti monastery, a leading Tibetan Buddhist institution that has been the scene of repeated protests by Tibetans against what they say is religious and cultural repression by Beijing.

At least 20 Tibetans have set fire to themselves in the past year to protest what they see as a lack of rights under Chinese rule, leading Beijing to impose virtual martial law, according to residents and exiled groups.

Many have been monks from Kirti, which has been under virtual lockdown since a young monk named Phuntsog set light to himself and died last March, sparking mass protests there.

Government and police officials in Aba refused to confirm the latest attempt when contacted by AFP.

It came as police in Washington arrested and briefly held activists who unfurled a banner on a bridge reading "Tibet Will be Free" during the visit of China's leader-in-waiting, Vice President Xi Jinping.

The activists, from the group Students for a Free Tibet, said they were later released after being issued citations with fines of about $250 each for trespassing and disorderly conduct.

The spate of suicide attempts has led Beijing to impose virtual martial law in Tibetan-inhabited areas of China, residents and exiled groups have said.

China has accused overseas groups and Tibet's exiled spiritual leader the Dalai Lama of fomenting unrest.

Tibetans have long chafed under China's rule over the vast Tibetan plateau, accusing Beijing of curbing religious freedoms and eroding their culture and language, and these tensions have intensified over the past year.

But Beijing insists that Tibetans enjoy religious freedom and have benefited from improved living standards brought by China's economic expansion.

Geng He, who fled to the United States with the couple's children in 2009, hoped the United States would seek answers on her husband's case during the visit by China's leader-in-waiting Xi Jinping who arrived Monday.

Gao, who has defended some of China's most vulnerable people including underground Christians and coal miners, was arrested in February 2009 and there has been no public sign of him except for a brief release in 2010.

"The government has lied to the family so many times in the past few years. They laugh at and play games with the family," Geng told AFP in a weekend interview.

"The whole thing is very strange. I don't have any way to know whether he's still alive," she said.

Chinese authorities have said little publicly about Gao despite the focus on his case overseas. In December, the official Xinhua news agency said that Gao had been sent back to prison for violating his terms or probation.

Gao's brother, Gao Zhiyi, said he went last month to the distant northwestern region of Xinjiang after receiving a letter saying Gao Zhisheng was jailed there but that he was turned away.

Geng said the family has had a series of mysterious contacts. She said that police inexplicably telephoned Gao's sister one day before the Xinhua report and asked if the long-missing lawyer was at her home.

Geng said Gao's brother was also visited by a robed man who gave a business card describing himself as a monk, but who later identified himself as a police officer.

Asked what her message would be for Xi, who is expected to be China's next president, Geng said: "Why is it that my husband, who has been trying to work for justice and people's rights -- things that are considered good in the US and many other countries -- has been persecuted and even disappeared?"

Geng broke down with emotion as she explained that she had trouble calling relatives back in China during the recent New Year's season.

"When my family is too afraid to pick up my calls, I just feel terrible. I don't feel I've done anything wrong, but they are so afraid," she said.

Geng plans to testify Tuesday about her husband's case before the US government's Congressional-Executive Commission on China, just after Xi holds talks at the White House with President Barack Obama.