Kathmandu has seen almost daily protests outside UN offices by Tibetan exiles who are demanding that the world body probe the causes of violent anti-Chinese unrest that has shaken Tibet.

This was the first time that protesters managed to elude a heavy police presence around the UN complex and scale the high walls, a witness said.

Some 18 teenage students wearing school uniforms jumped into the compound and were inside a UN building, the reporter said, adding: 'Police are waiting for them at the entrance' to the complex.

'We want the UN to investigate China's suppression of the Tibetans,' student Tenzing Topjor, 15, said before being chased away by police.

Around five teenage students were among the 40 protesters who were detained and driven away in police vans, the reporter said.

'We have no idea how they got into the UN complex,' said a police officer at the site who did not wish to be identified.

Monasteries in Lhasa remain closed
All monasteries in Lhasa remained closed on Friday following riots that engulfed the Tibetan capital, a government official said, amid reports that monks had been locked inside for two weeks.

'None of the monasteries in Lhasa are open... it's hard to say when they will reopen. This issue is beyond our powers,' an official with the Lhasa Tourism Administration, who declined to be named, said by phone.

The monasteries were closed in the lead-up to, and following, violent unrest on March 14 that saw Tibetans take to the streets in protest against China's 57-year rule of their devoutly Buddhist Himalayan homeland.

Ahead of the riot, monks were involved in four days of peaceful protests in Lhasa that were initially held to mark the anniversary of a failed 1959 uprising against Chinese rule.

The unrest in Lhasa spread to other areas of western China with Tibetan populations, prompting authorities to send in massive deployments of security forces to quell the unrest.

China says rioters killed 18 innocent civilians, including three ethnic Tibetans, and two police officers in the protests.

Exiled Tibetan leaders have put the death toll from the Chinese crackdown at between 135 and 140, with monks among those killed, and another 1,000 people injured.

China's atheist communist government has always regarded the monasteries as a potential source of opposition to its rule of Tibet, and has blamed exiled Tibetan spiritual leader the Dalai Lama for fomenting the latest unrest.

On Thursday, monks at one of Tibetan's holiest shrines, the Jokhang temple in the heart of old Lhasa, embarrassed Chinese authorities when they spoke out in front of foreign reporters against China's rule of Tibet.

'We want the Dalai Lama to return to Tibet, we want to be free,' the monks yelled.

The 26 foreign reporters were brought in by the Chinese government for a three-day trip as part of efforts to show that the situation in Lhasa had returned to normal.

The Wall Street Journal, which was on the tour, reported on Friday that a government official in Lhasa had confirmed that monks in the city's monasteries had been locked inside since March 14.

The newspaper reported that armed police had surrounded the three main monasteries in Lhasa - Drepung, Ganden and Sera - and that the foreign media delegation had not been allowed into them.

It also cited the Tibetan government's deputy chairman, Pela Trilek, as confirming that 414 people, mostly Tibetan and including monks, had been detained.

The International Campaign for Tibet, citing sources in Lhasa, reported that monks who had tried to leave Sera monastery had guns pointed at their heads and were ordered to go back.

Monks who have expressed support for the Dalai Lama, who fled Tibet following the failed 1959 uprising, have previously suffered harsh punishment.

In one of the most well-known cases, 14 nuns in 1993 secretly recorded songs on a tape about the Dalai Lama while serving sentences in Tibet's Drapchi prison.

The tape was smuggled out of prison to the West. As a result the sentences of the women, who became known as 'the singing nuns,' were extended.

China has ruled Tibet since 1951, after sending in troops to 'liberate' the region the previous year. -- AFP