More than 100 Tibetan exiles have begun a march from India to Tibet to protest against Chinese rule in the region.
It is not clear what route the marchers are taking
The marchers left Dharamsala on the 49th anniversary of the Dalai Lama's escape from Tibet after a failed uprising against Chinese rule.
The Dalai Lama, Tibet's spiritual leader, has called for greater pressure on China over its human rights record.
In Nepal, at 1,000 Tibetan exiles have clashed with police in Kathmandu while trying to march to the Chinese embassy.
Tibet activists are hoping to use China's hosting of the Olympics to publicise their cause.
Before the marchers in India set off, the Dalai Lama said he approved of China hosting the games because it provided the world with a chance to pressurise the Beijing government to uphold the Olympic ideals of freedom of speech and equality.
Protesters in Nepal were arrested
"China should prove herself a good host by providing these freedoms. Therefore, besides sending their athletes, the international community should remind the Chinese government of these issues," the Dalai Lama said.
The Dalai Lama heads the Tibetan government in exile in Dharamsala, a northern Indian hill town.
In hard-hitting remarks, the Dalai Lama said that "repression continues to increase with numerous, unimaginable and gross violations of human rights, denial of religious freedom and the politicisation of religious issues" by China.
The Dalai Lama has previously been seen as less radical than some exiled activists, says the BBC's Chris Morris - for example no longer advocating full independence for Tibet.
But his call for greater freedoms in the region is a demand that China will hear with increasing frequency in the Olympics year, says our correspondent.
Tibetan exile groups say the march is to be one of several protest events in the run-up to the games in Beijing in August.
"It could potentially be our biggest protest since we came into exile in 1959. We are determined to go home and nobody could stop us from doing that," Lobsang Yeshi, one of the co-ordinators said.
Organisers say they represent tens of thousands of Tibetan exiles, and want to draw attention to what they see as Chinese suppression of Tibetan identity.
The precise route of the march has not yet been decided, and organisers will not say exactly where or when they will attempt to cross into Tibet.
Meanwhile police in the Nepalese capital, Kathmandu, say that up to 80 protesters have been arrested.
Eyewitnesses told the BBC between 1,000 to 3,000 Tibetan exiles and their supporters gathered at a large Tibetan Buddhist shrine, including many monks and nuns.
The BBC's Charles Haviland in Kathmandu says that police barred the way when some protesters tried to march towards the Chinese embassy, which lies in a different suburb.
One protester said they charged them with batons and used tear gas and that the demonstrators threw stones.
Police sources later told the BBC calm had returned to the site, but admitted that monks were shouting slogans outside the police station, where scores of the demonstrators were being held.
Protests by Tibetans have also been held in other parts of the world, including the Greek capital, Athens, where protesters were prevented from getting into the site of Olympia, the birthplace of the ancient Olympic Games.