International Olympic Committee president Jacques Rogge said on Thursday that protests dogging the torch relay had left the games in crisis and urged Beijing to honour pledges to improve human rights.
After hundreds of baton-wielding police shielded the Olympic torch through San Francisco to avoid the chaos of earlier legs in Europe, Rogge said he was still confident Beijing would host a successful games in August.
He said he was "saddened" by the violent protests in London and Paris, but believed the stop in San Francisco had been an improvement and that the relay would not be cut short.
"It was, however, not the joyous party that we had wished it to be," Rogge told a joint meeting of the Association of National Olympic Committees and the IOC's executive board.
He said sports leaders should seek to reassure athletes.
"Tell them that whatever they have seen and heard, the games will be very well-organised. Tell them that we will rebound from this current crisis," he said.
Rogge noted at a press conference that Chinese officials had promised when bidding to host the 2008 Olympics that being awarded the games would "advance the social agenda of China, including human rights."
"This is what I would call a moral engagement rather than a juridical one," he said. "We definitely ask China to respect this moral engagement."
Protesters highlighting China's rule of Tibet and other human rights issues severely disrupted the torch relay earlier this week in London and in Paris, where officials had to extinguish the flame several times.
There was no major trouble in San Francisco after organisers shortened the course for the only US leg, switched the route at the last minute and set up a multi-layered security cordon against a growing number of demonstrators.
Within seconds of the start, the first runner disappeared into a dockside warehouse. The torch was then borne on a shorter route through the city before being taken to the airport for its next flight to Buenos Aires.
San Francisco Mayor Gavin Newsom said it was a tough decision to change the route, which left many supporters disappointed at not seeing the flame.
"I'm sorry. I wanted this to be a perfect event. I want this world to be a perfect world. I want what happened in Paris not to have happened. I want what happened in London not to have happened," he said.
Police said there were some minor incidents but no arrests, although an AFP photographer saw a pro-Tibet protester led away in handcuffs after a standoff with pro-China supporters.
A Chinese-born US citizen triggered angry scenes when he tried to unfurl a Tibetan flag yards away from the starting point.
World leaders have faced mounting calls from rights groups to boycott the opening ceremony of the Games in protest at China's recent crackdown on Tibet, which it has ruled since 1951.
German Chancellor Angela Merkel is not going, and British Prime Minister Gordon Brown's office said he also would not attend, although it stressed his plans had not changed.
"He's never been going to the Olympic opening ceremony. We have always said he's going to the closing ceremony," a spokeswoman for his office told AFP, as London will be hosting the next Games in 2012.
The White House again refused to say if US President George W Bush would go, saying it was "extremely premature" to predict his schedule for August.
Bush himself vowed in an interview to be broadcast Friday to press China on human rights at the Olympics, but chafed at calls for a boycott.
"Nobody needs to tell old George Bush that he needs to bring religious freedom to the doorstep of the Chinese, because I've done that now for -- I'm on my eighth year doing it," he told EWTN television, a Catholic network.
The 15-member IOC executive board begins a two-day meeting later Thursday where the torch relay will be reviewed, amid suggestions future versions could be run only inside the host country.
The Olympic flame is to travel through 20 countries on its round-the-world journey from Greece, arriving in China in early May. (AFP)
Olympic chief urges China to act on human rights