Exiled Tibetan leaders have put the death toll from the Chinese crackdown at 135-140 people, with another 1,000 injured and many detained.
China says Tibetan rioters killed 18 civilians and two police officers.
Protests began in the Tibetan capital Lhasa on March 10 and escalated into rioting there four days later.
Earlier, on Tuesday, the US rejected China's charges that Dalai Lama was backing suicide attacks, calling him a "man of peace" with whom Beijing should speak.
Asked if Washington agreed with Beijing's allegations, Tom Casey, the state department's deputy spokesman, said: "There's absolutely no indication that he wants to do anything other than have a dialogue with China to discuss how to deal with some of the serious issues there."
Chinese police on Tuesday said Tibetans were planning suicide attacks as part of a campaign in the run-up to the 2008 Beijing Olympics to push for independence in their homeland.
"To our knowledge, the next plan of the Tibetan independence forces is to organise suicide squads to launch violent attacks", said Wu Heping, Chinese public security ministry spokesman.
"They fear neither bloodshed nor sacrifice".
Wu linked the alleged suicide attack plans, denied by Tibet's government-in-exile in India, to the Dalai Lama and said explosives had been found in Buddhist monasteries in Tibet.
The Dalai Lama, who won the Nobel Peace Prize in 1989, has repeatedly denied orchestrating the unrest, spoken out against the protests when they turned violent, and denied he wants independence for his homeland.
Bush phoned Hu Jintao, his Chinese counterpart, last week to express concern over the unrest and urge China to reopen talks with the Dalai Lama, who Chinese authorities blame for orchestrating the unrest.
Bush has resisted calls to boycott the opening ceremony of the Olympic games in August to express dissatisfaction with China's handling of the Tibetan unrest.
|China's neighbours, such as Nepal, have been|
rocked by pro-Tibet demonstrations [Reuters]
A bill was introduced in the House of Representatives on Tuesday by Thaddeus McCotter, chairman of the policy committee of Bush's own Republican party, calling on him not to attend the ceremony.
In addition, 15 legislators from both the Republican and Democratic parties asked Bush in a letter to "renounce your decision to attend the Olympics in China and urge the Chinese government to change its policies and begin to respect international standards of human rights".
Nancy Pelosi, the house speaker, has also urged Bush to boycott the opening ceremony.
With just over four months until the opening ceremony, Amnesty International, the London-based human-rights organisation, said in a report on Tuesday that it was increasingly unlikely the games would improve rights in China.
It urged the International Olympic Committee and world leaders to speak out publicly against rights violations.