Mrs Clinton said it was a time for Mr Bush to show presidential leadership
US presidential hopeful Hillary Clinton has called on President George W Bush to boycott the Olympic opening ceremony unless China acts on human rights.
Senator Clinton cited violent clashes during recent unrest in Tibet and lack of pressure by the Chinese on Sudan "to stop the genocide in Darfur".
Her Democratic rival, Barack Obama, said he had expressed his concerns about the Games to Mr Bush.
Anti-Chinese protests have disrupted the Olympic torch relay in Europe.
Demonstrators in the US city of San Francisco, where the torch is due to arrive on Wednesday, climbed the cables of the Golden Gate Bridge on Monday to hang pro-Tibet banners and a Tibetan flag.
Police have said security will be tight along the six-mile (10km) route to be followed by the torch along San Francisco Bay, in an attempt to prevent further disruption by protesters.
The Olympic flame is being carried through 20 countries before arriving for the Beijing Games in August.
Mrs Clinton said Mr Bush should not attend the ceremony "absent [without] major changes by the Chinese government".
Her call came five days after the White House rejected calls in the Democratic-led US Congress for Mr Bush to miss the Beijing opening ceremonies.
The New York senator, who is competing with Mr Obama to be the Democratic Party's choice to run for president in November, urged Americans to "stand strong in support of freedom of religious and political expression and human rights".
She said that violent clashes in Tibet and the "failure of the Chinese government to use its full leverage with Sudan to stop the genocide in Darfur" were opportunities for presidential leadership.
In a statement on Monday, Mr Obama said he was "deeply disturbed by the recent events in Tibet" and had expressed his concerns both in public and to Mr Bush.
If China did not take quick steps to respect rights and freedoms in Tibet, "there should be consequences", he added.
'Sport, not politics'
Mr Bush has previously said he will attend the Olympics because it is a sporting and not a political event.
Pro-Tibet protesters hung banners on San Francisco's Golden Gate bridge
White House spokesman Tony Fratto told reporters that the president had not altered his stance on the Olympics.
He added that the Bush administration's concerns over China's human rights record were also unchanged.
"We have never been afraid to express those views either directly by the president or the president's senior advisers when they travel to China and publicly," he said.