A previously unknown militant group claimed responsibility on a militant Web site for the murder of a U.S. diplomat in Sudan on New Year's Day, announced the SITE Intelligence Group which monitors extremist sites.

There was no way to authenticate the statement by the group calling itself Ansar al-Tawhid (Companions of Monotheism), a fairly generic-sounding name for an Islamic extremist organization.

"The soldiers of Tawhid carried out an operation of killing the American diplomat and his Sudanese driver who sold his religion for few benefits of life, in the section of Al-Riyadh in eastern Khartoum," read the translation provided by SITE.

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John Granville, an official for the U.S. Agency for International Development, was being driven home at about 4 a.m. Tuesday when another vehicle cut off his car and opened fire before fleeing the scene, according to the Sudanese Interior Ministry.

The diplomat's driver, Abdel-Rahman Abbas, was also killed. Granville, who was hit by five bullets but initially survived, died after surgery, said the embassy.

Sudanese officials insist the shooting was not a terrorist attack, but the U.S. Embassy said it was too soon to determine the motive. There has been no claim of responsibility, and U.S. and Sudanese officials investigating the shooting have not specified any suspects.

FBI investigators are currently in Khartoum working with Sudanese security agencies to investigate the attack, which was the first assassination of a U.S. diplomat in Sudan since 1973.

Al-Qaida has shown little overt presence in Sudan in since the Sudanese government threw out Osama bin Laden in the late 1990s.

Last year, for the first time, a group calling itself al-Qaida's branch in Sudan claimed responsibility for the slaying of a Sudanese newspaper editor accused by some of blasphemy over articles run in his paper.

But the Sudanese government said the claim was fake and that the editor was killed by Darfurians angry over the paper's coverage of the conflict.