The six men, aged between 16 and 27, were held at a remote Himalayan village 120 kilometres (74 miles) northeast of the capital Kathmandu after crossing into Nepal on foot.

"They were arrested before dawn on Tuesday by the local police," said Umesh Raj Joshi, deputy superintendent of Dolakha district, which borders Tibet. "We have already handed them over to the immigration authorities."

Thousands of Tibetans used to make the difficult and dangerous journey to Nepal every year, fleeing political and religious repression in China.

They were previously given safe passage through Nepal under an informal agreement with the UN refugee agency, which helped them to travel on to India, where the Tibetan spiritual leader the Dalai Lama lives in exile.

But their numbers fell sharply after 2008 riots in Tibet led China, which is a major donor to Nepal, to strengthen border security and increase pressure on authorities in Nepal to stem the flow.

The police declined to reveal exact figures but Tibetan groups in Kathmandu said they had information about only a handful of arrests in the last year, none of which have been confirmed.

US embassy cables released by WikiLeaks last year suggested that China paid Nepalese police to detain Tibetans.

Nepal, home to 20,000 Tibetan exiles who were given refugee status before 1989, denied the accusation.

Shouting "Free Tibet" and "China is a liar," more than 20 Tibetans and supporters criticized Beijing for celebrating the 60th anniversary of the territory's incorporation but banning observance of the Dalai Lama's birthday.

"We wanted to show the world that the Chinese propaganda is not fooling anyone," said Tenzin Dorjee, executive director of Students for a Free Tibet, the advocacy group that organized the protest.

"Tibet has a stronger desire for freedom now than ever," he said. "We need to show the world that Tibet can't be stopped by the Chinese government."

In Washington's high-security embassy district, the activists handed out fliers called "17 Points of Disagreement," a play on the China's "17 Points of Agreement for the Peaceful Liberation of Tibet" in 1951.

China sent troops into Tibet in 1950 and nine years later the Dalai Lama, the predominantly Buddhist region's spiritual leader, fled into exile in India. The Dalai Lama has since built a wide global following and is visiting Washington to lead a religious ritual known as a Kalachakra.

The Dalai Lama says he is peacefully seeking greater rights for Tibetans. The US State Department in its latest human rights report charged that China has severely restricted freedoms in Tibet and other ethnic minority regions.

Beijing says it has brought progress to Tibet and in a white paper Monday wrote that Tibetans have been linked to China's majority Han ethnic group "since ancient times."