KHARTOUM - A U.S. government aid official was critically wounded in a shooting attack on an embassy vehicle in Khartoum on Tuesday and his Sudanese driver was killed, Western diplomatic sources said.

"What we have heard is that a driver and a U.S. official, sometime a little after midnight, were heading home. The driver was shot and died on the spot and the U.S. official was shot and critically injured," one of two diplomatic sources told Reuters, speaking on condition of anonymity.

Both sources identified the U.S. official as an American man working for the U.S. Agency for International Development (USAID) in Khartoum, but could not immediately give his full name. The driver also worked for USAID, they said.

"The American man is now in hospital ... and needs blood. He lost so much blood," the second source said, adding that the man remained in Khartoum.

The shooting came a day after U.S. President George W. Bush signed into a law a measure aimed at facilitating divestment from Sudan for those who want to cut investments due to the conflict in Darfur in the country's west.

The U.S. government also warned citizens in Sudan in a warden message in August that it had received credible information that "an extremist group based in the country may target U.S. government interests or facilities".

Al Arabiya television reported that the attack took place in a main street in the capital Khartoum, and said the U.S. official had been shot in the chest.

A U.S. public diplomacy officer with the U.S. embassy in Khartoum, Walter Braunochler, said in a telephone interview with CNN that it was "too early to tell" if the shooting was a militant attack or a street crime.

OIL SECTOR

Al Arabiya television said there was no immediate claim of responsibility and quoted the Sudanese Foreign Ministry as saying the shooting was the result of a traffic dispute. Officials from the Ministry could not be immediately reached.

Washington has long had tense relations with Khartoum due to the conflict in the country's west, which Bush has labelled as genocide. The Sudanese government has rejected that charge.

The measure Bush signed into law on Monday allows states, local governments, mutual funds and pension funds to cut investment in companies doing business in Sudan, particularly its oil sector.

Some 20 U.S. states have initiated divestment efforts because of the ethnic and political conflict in Darfur, which international experts say has taken roughly 200,000 lives and displaced some 2.5 million since rebels took up arms against the government in 2003. Khartoum says only 9,000 have died.

On Monday a joint U.N.-African Union (AU) force took charge of peacekeeping in Darfur.

The force replaces a struggling AU mission. The plan is for it ultimately to comprise 20,000 soldiers and 6,000 police, but numbers are currently only about a third of those levels.

"My administration will continue its efforts to bring about significant improvements in the conditions in Sudan through sanctions against the government of Sudan and high-level diplomatic engagement and by supporting the deployment of peacekeepers in Darfur," Bush said in a statement on Monday.