A leading international human rights watchdog has asked Chinese government to permit immediate access to independent monitors to the people detained in Tibet and adjoining provinces in the aftermath of protests so as to give the world confidence that detainees were not being tortured or mistreated.

"Given the long and well-documented history of torture of political activists by China's security forces there is every reason to fear for the safety of those recently detained," said Brad Adams, Asia director at Human Rights Watch.

"Only by giving access to independent monitors can China give the world some confidence that detainees are not being tortured or mistreated," Adams added.

The Chinese authorities have not specified the number of detainees, but unconfirmed reports suggest that hundreds have been arrested.

Human Rights Watch and others groups have previously alleged torture and ill-treatment of detainees in Tibet, especially those accused by the Chinese authorities of "separatist activities."

Chinese officials had announced that those who had been involved in the protests must "surrender" to police by midnight on March 16 and that they would be shown leniency if they did so.

The officials insisted that the detention of protesters was necessary to ensure public security.

The Chinese government, the HRW said, has virtually sealed off Tibet by expelling or turning away foreign tourists and journalists.

The Chinese government has long banned independent human rights observers from Tibet and punishes Tibetans who send information out of the country regarding the human rights situation, it added.

"The exclusion of independent monitors and expulsion of foreign media from Tibet only suggest that China wants to retaliate against these protesters unfettered by global scrutiny," said Adams.

"China is in direct violation of its commitment to the International Olympic Committee to allow foreign journalists free access to the whole country, a point the IOC should be making publicly if it is to retain any credibility," he added.