China's human rights record is getting worse, not better, because of the Beijing Olympics, a rights group says.

According to Amnesty International, China is clamping down on dissent in a bid to portray a stable and harmonious image ahead of the Games in August.

It urged the International Olympic Committee (IOC) and world leaders to speak out against abuses, including China's handling of protests in Tibet.

US President George W Bush is facing calls to boycott the Games' opening.

"It would be clearly inappropriate for you to attend the Olympic Games in China, given the increasingly repressive nature of that country's government," a group of 15 US politicians wrote in a letter to Mr Bush on Tuesday.

Mr Bush has said he plans to attend the ceremony but Germany's Angela Merkel says she will not. French President Nicolas Sarkozy has not ruled out a boycott.

An IOC team is currently in Beijing to assess its readiness for the Games.

'Beyond reach'

In a report entitled China: The Olympics Countdown, the London-based group said the Olympics had failed to act as a catalyst for reform in China.

It is increasingly clear that much of the current wave of repression is occurring not in spite of the Olympics but actually because of the Olympics Amnesty International report

"Unless the Chinese authorities take steps to redress the situation urgently, a positive human rights legacy for the Beijing Olympics looks increasingly beyond reach," it said.

"It is increasingly clear that much of the current wave of repression is occurring not in spite of the Olympics but actually because of the Olympics."

Activists and dissidents had been targeted as part of an apparent pre-Olympics clean-up, it said, with many under some form of detention.

Journalists, both domestic and foreign, were still prevented from reporting freely.

The group also called on world leaders to speak out on the situation in Tibet, calling a failure to address the issue "tacit endorsement" of human rights abuses.

It accused Chinese troops of using lethal force on Tibetan protesters and urged China to release information about those who had been detained, saying it feared for their safety.

'Prejudice'

On Tuesday, ahead of the publication of the report, China hit out at Amnesty and said any attempt to pressure Beijing over the Olympics would fail.

"The organisation holds prejudice against China, so you can imagine what kind of report it will release," foreign ministry spokeswoman Jiang Yu said.

Public Security Ministry spokesman Wu Heping also said that Tibetan "independence forces" were planning to launch suicide attacks as part of a wider uprising - a move he blamed on the Dalai Lama.

China says 18 civilians and two police officers died in the unrest in Tibetan and neighbouring provinces inhabited by Tibetans that began on 10 March.

Tibetan groups outside China put the death toll at up to 140, a figure that includes Tibetans they say were killed by Chinese security forces.

All claims about the unrest are difficult to verify because the Chinese government has mostly barred foreign journalists from these sensitive areas.