US embassy staff in Khartoum were making final preparations over the weekend for their forthcoming withdrawal. About 30 embassy employees are due to leave by the end of the week, although the US insists it is not breaking diplomatic relations with Sudan.
Kenya has agreed to accept the US ambassador, Mr Timothy Carney, and a handful of other diplomats who will operate a temporary diplomatic office in Nairobi. There have been reports of threats to the embassy staff.
"We're suspending our presence out of concern for the safety of our personnel, a US diplomat said. "There's been no one development which has prompted our decision.
"We've had a long standing concern over Sudan harbouring terrorist groups. It's dangerous for us here, and it will continue to be dangerous for as long as the Sudanese government fails to curb the activities of terrorist groups based here."
Sources close to the embassy indicate that US diplomats also have been worried by what they perceive as growing anti Americanism in the Sudanese press.
The embassy spokesman dismissed as "totally coincidental" the fact that the announcement of a withdrawal came at the same time as a UN Security Council resolution demanding the Sudanese hand over three men suspected of trying to kill President Mubarak of Egypt last year.
Mr Mubarak escaped unharmed after an attempt on his life in Addis Ababa, the Ethiopian capital, last June. Sudan has consistently denied involvement in the attack.
The US says the threats to its embassy staff in Khartoum come from both Sudanese and "non Sudanese elements", a catch all phrase denoting Palestinian and other Islamic fundamentalist groups.
The US, which has had Sudan on its list of state sponsors of terrorism since 1993, reports the existence of up to 20 terrorist training camps inside the country. The camps, at which foreign militants allegedly are trained in political assassination and other subversive acts, are said to be moved frequently to outwit spy satellites.
The UN is backing assertions by both Egypt band Ethiopia that Sudan was behind the assassination attempt on President Mubarak last year. Sudan has been given 60 days to hand over the three men alleged to have taken part in the attack.
The Sudanese Foreign Minister, Mr Ali Osman Mohammed Taha, has said Sudan is doing everything possible to help Egypt and Ethiopia track down the men who opened fire on the Egyptian leader. He also has described the US embassy pullout as "regrettable" and has warned that the UN resolution is a prelude to the imposition of sanctions against Sudan.
The Sudanese government acknowledges that one of the three men wanted in connection with the attempt to kill Mr Mubarak passed through Khartoum last year. It denies, however, that it has any trace of the other two men.