Reports of protests
The Dalai Lama, the Tibetan spiritual leader who is based in the north Indian hill town of Dharamshala, said he had heard about the new protests.
"I heard people of Lhasa came out in protest again today," he said, without providing details.
An aide to the Dalai Lama said the exiled government was still trying to obtain more information.
He said that no firm details were available on the number of protesters.
"We received some calls that there are demonstrations taking place in Lhasa," said Tenzin Taklha, deputy secretary to the Dalai Lama.
"We are still trying to confirm this and get the news out."
The reportd protests come as diplomats complete a two-day visit, organised by China, to defuse criticism of its crackdown.
The tour had been offered to diplomats by the Chinese authorities and was a closely monitored affair, a Western embassy representative said.
Demonstrations earlier in March erupted
into widespread rioting [AFP]
A US diplomat on the tour urged the Chinese government to grant the media and foreign envoys more access to Tibet.
"The trip was heavily scheduled, and neither the US nor other participants were able to deviate from the official itinerary," the embassy said in a statement.
The London-based International Campaign for Tibet said it had heard from three sources that security forces had surrounded Lhasa's main temples, Jokhang and Ramoche.
"I think people in Lhasa may have been aware of the diplomats' visit, just as they were aware of the journalists' visit," said Kate Saunders, the group's spokeswoman.
EU foreign ministers on Saturday urged China to hold a dialogue on Tibetan cultural and religious rights, but they have avoided linking the issue to the Olympics.
The new protests come as the Olympic flame, on Saturday, arrived in Athens, the Greek capital, in advance of its symbolic handover to Beijing Games organisers.
The torch arrived flanked by police. A helicopter kept guard throughout the day on a route draped with Greek and Chinese flags and blocked to traffic.
Several dozen members of Tibetan and human-rights groups staged a peaceful protest against Chinese repression in Tibet and the holding of the Olympics in Beijing in August.
Activists in Tibet began rallying on March 10 to mark a failed 1959 uprising against Chinese rule.
Demonstrations erupted into widespread rioting in Lhasa on March 14, and spread to neighbouring Chinese provinces populated by Tibetans just months before the opening of the Beijing Olympics.
Chinese media has portrayed the March 14 violence as a riot by a Tibetan mob beating up innocent people, many of them ethnic Chinese.
Beijing says the rioters killed 18 innocent civilians and two police officers.
Exiled Tibetan leaders have put the death toll from the Chinese crackdown at between 135 and 140 Tibetans, with another 1,000 people injured and many detained.
Earlier on Saturday, the Dalai Lama accused the Chinese government of a policy of "demographic aggression", which he said was seeing an increasing number of ethnic Chinese move into the region and that Tibetan culture was being eroded.
He called the shift in population a "form of cultural genocide".
"There is evidence the Chinese people in Tibet are increasing month by month," the Tibetan spiritual leader said in New Delhi before returning to Dharamsala.
In Lhasa there are now 100,000 Tibetans, but twice as many outsiders, he said.
The majority of those are Han Chinese - the country's ethnic majority.