Oscar-winning film director Steven Spielberg [Images] withdrew on Tuesday as an artistic adviser to the 2008 Summer Olympics [Images] in Beijing [Images] over China's policy on the conflict in Sudan's Darfur region.

"I find that my conscience will not allow me to continue business as usual," Spielberg said in a statement issued on a day when Nobel Peace laureates sent a letter to China's President Hu Jintao urging a change in policies toward its ally Sudan.

"At this point, my time and energy must be spent not on Olympic ceremonies, but on doing all I can to help bring an end to the unspeakable crimes against humanity that continue to be committed in Darfur," he added.

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China is a leading oil customer and supplier of weapons to Sudan and is accused by critics of providing diplomatic cover for Khartoum as it stonewalls international efforts to send peacekeepers into Darfur.

In April, Spielberg wrote a letter to Chinese President Hu Jintao adding his voice to the chorus of people who have protested China's involvement with the Sudanese government over the crisis in Darfur. At that time, Spielberg had asked to meet with Hu, but the President failed to respond.

In his statement on Tuesday, Spielberg said Sudan's government shouldered the bulk of responsibility for "these ongoing crimes" in Darfur but said China "should be doing more to end the continuing human suffering there."

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Earlier on Tuesday, nine Nobel Peace Prize laureates -- including Archbishop Desmond Tutu, Elie Wiesel and Jody Williams -- sent a letter to Hu urging China to uphold Olympic ideals by pressing Sudan to stop atrocities in Darfur.

"As the primary economic, military and political partner of the Government of Sudan, and as a permanent member of the United Nations Security Council, China has both the opportunity and the responsibility to contribute to a just peace in Darfur," said the letter.

"Ongoing failure to rise to this responsibility amounts, in our view, to support for a government that continues to carry out atrocities against its own people," said the letter, released on a day of events by the Save Darfur Coalition.

The letter was also signed by US politicians, Olympic medallists and entertainers and delivered to Chinese embassies and missions as part of events in the United States and Europe staged to mark six months before the August 8-24 Olympics.

UNDERWRITING GENOCIDE

In more than four years of conflict in Sudan's western region of Darfur, 200,000 people have died and 2.5 million have been driven from their homes, according to estimates from international experts. Khartoum says 9,000 people have died.

Sudan's government, in its largest offensive in months, attacked three towns in Darfur on Friday, forcing about 200,000 people from their homes and leading thousands to flee into neighbouring eastern Chad.

The United States pressed Sudan to stop the campaign.

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US actress Mia Farrow, who has led the coalition's global campaign to press China to change its policies, gathered a crowd outside the Chinese mission to the United Nations in New York as she tried to deliver the letter.

"China hopes that these games will be its post-Tiananmen Square coming out party. But how can Beijing host the Olympic Games at home and underwrite genocide in Darfur?" she said, stuffing the letter under the mission door after her knocks went unanswered.

The letter to Hu acknowledged Chinese support for a UN Security Council resolution calling for deployment of a UN-African Union peacekeeping force in Darfur.

"However, we note with dismay that the Chinese government worked to weaken the resolution before it passed," it said. The letter said China doubled its trade with Sudan in 2007 and continued its military relationship with the African country.

Jody Williams, a US citizen who won the prize in 1997 for her campaign against land mines, said she and fellow female laureates had formed the Nobel Women's Initiative in 2006 to focus on conflicts and particularly their impact on women.

Mass rape has been a weapon of warfare in Darfur and in Myanmar, the former Burma, another Chinese-backed regime.

"In Darfur and in the case of Burma, China is the eight-jillion-ton elephant in the room and needs to use some of its weight in a positive way," Williams said by telephone from Virginia.

The Save Darfur Coalition said it staged similar events in Britain, Portugal and Italy [Images] on Tuesday and planned more protests in Nigeria, France [Images], Australia and elsewhere.

The campaign has so far not called for a global boycott of the Beijing games, although activists advocate not attending or watching the Beijing Olympics on television.

China's Embassy had no immediate comment. But last month, the ruling Chinese Communist Party's flagship newspaper and foreign ministry said China would never submit to pressure from groups trying to use the Olympics to change Chinese policy.