BEIJING — A teenage monk set himself on fire to protest China's rule in the nation's southwest, exile groups said Tuesday, as police in Washington arrested Tibet activists during a visit by China's vice president.

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.