Sudan will have to accept non-African troops in a U.N.-authorized peacekeeping force for Darfur or face the prospect of new United Nations sanctions, a senior U.S. official said Tuesday.

Although efforts will be made to ensure that Africa contributes a large percentage of the 26,000-strong mission, the continent does not have enough trained soldiers to fully staff the force and Sudan will be penalized unless it drops objections to non-African participation, said Andrew Natsios, the U.S. special envoy for Sudan.

President Bush has made ending the Darfur conflict a U.S. foreign policy priority but the United States is reluctant to provide troops itself for the force, given military commitments in Iraq and Afghanistan. Instead, Washington is likely to contribute logistics and transportation to the mission.

Secretary of State Condoleezza Rice in June ordered U.S. ambassadors to ask their host countries to contribute to the hybrid force, Natsios said.

"We are going to try ... to recruit from Africa, but it's very clear from already talking to African leaders and African militaries that there are not enough African troops who are trained for peacekeeping operations to make up this force," he told reporters in a conference call. "We are going to have to go outside of Africa."

The Sudanese government is adamantly opposed to non-Africans playing any major role in the hybrid U.N.-African Union operation that was authorized by the U.N. Security Council on July 31 and will be made up of 20,000 peacekeepers and 6,000 civilian police.

Disagreements over the composition of the mission were a major reason the authorization was delayed for months despite mounting pressure on Khartoum to accept it to help end nearly four years of internal conflict in which more than 200,000 people have died and 2.5 million have been displaced.

Natsios, however, said that in finally agreeing to the mission, Khartoum had opened the door to non-African participation, although he stressed that in accordance with Sudan's demands command of the force had been given to a senior Nigerian general.

"We expect the Sudanese government to implement what they have agreed to, which is if we can't get sufficient trained troops, we will go outside of Africa, which I have to say I expect will happen," he said, warning of consequences if Sudanese President Omar al-Bashir's government balks.

"If there is an attempt to renegotiate what was negotiated already with the Sudanese government, then we will introduce a sanctions resolution before the U.N," Natsios said.

It was not immediately clear how many non-African troops and police would be required to fully staff the hybrid mission but there are now 7,000 African personnel in the A.U. mission in Darfur, most of which are expected to stay on after its command changes on or before a Dec. 31 deadline.

Nigeria and Rwanda have offered to deploy another battalion each, about 1,600 troops total, and at least four other African nations have said they are considering sending soldiers, according to U.S. and U.N. officials. Still, they note, more contributions will be needed.

Among the suggestions to make up the shortfall in a way least objectionable to the Sudanese is to ask Muslim nations such as Bangladesh, Indonesia and Pakistan that have contributed peacekeepers to other U.N. missions in the past for help, the officials said.

The U.N. Peacekeeping Department and the new Department of Field Support issued a preliminary list of countries that have offered military and police personnel. It includes a large number of countries from Africa, several from Asia, one from the Middle East and none from the West.

"We are hitting the target of a predominantly African force, and we're very pleased about that," said Assistant Secretary-General Jane Holl Lute, acting head of the Department of Field Support.

The list of potential troop contributors includes Burkina Faso, Djibouti, Ethiopia, Egypt, Nigeria, Rwanda, Tanzania, Uganda, Bangladesh, Jordan, Malaysia, Nepal and Thailand. The list of countries offering at least 50 police officers includes Bangladesh, Burkina Faso, Ghana, Egypt, Indonesia, Nepal, Nigeria and Pakistan.

The U.N. stressed that these countries may or may not be included in the final force, which must be decided by Aug. 30 under the terms of the U.N. resolution.

Meanwhile, the State Department reacted coolly to an offer by Hollywood actress Mia Farrow, who has traveled to Darfur as a UNICEF goodwill ambassador, to give up her freedom to guarantee safe passage of an ailing Darfur rebel leader who fears for his life if he leaves a U.N. hospital where he is being treated.

The department's deputy spokesman Tom Casey said officials understood that many Americans, including celebrities, have "strong feelings" about Darfur but suggested Farrow's offer was naive, would not help and might tie down U.S. diplomatic resources.

"I certainly know our consular officials in Sudan would probably not appreciate having any American citizen prisoners there," he told reporters.

"While I think we all appreciate the kinds of gestures that are represented by individuals trying to make these kinds of statements, what we really want to focus our attention on is moving forward with the deployment of the hybrid force ... and then also trying to see that some of the political negotiations ... produce the kind of progress that allows us to ultimately have a political solution there."