(CNN) -- A group calling itself the Partisans of Monotheism in Sudan claimed responsibility Friday for the shooting death of an American diplomat and his driver early New Year's Day.
John Granville, seen in an undated family photo, was shot to death in Sudan Tuesday.
"The soldiers of monotheism carried out their operation in killing the U.S. diplomat John Micahel Granville and his Sudanese driver, who sold his faith for nothing in this earthly life, ... in Riyadh neighborhood east of Khartoum," the group said in a statement posted in Arabic and English on several Islamist Web sites. The group misspelled Granville's middle name, which is Michael.
The Web sites reported the group, also called Ansar Al-Tawhid, is new.
CNN cannot independently verify the authenticity of the statement or the legitimacy of the group.
The State Department was unaware of the claim, spokesman Sean McCormack said Friday, adding that the investigation into the deaths is in the initial stages.
Jane Granville, John Granville's mother, said she had no interest in discussing the claim of responsibility. Watch diplomat's body being returned »
"That is not going to help bring John back, or his driver, and I really -- that is of no interest to me," she told CNN in an exclusive interview. Watch Jane Granville describe her son's work in Africa »
Granville's body was expected to arrive in the United States Friday afternoon, with a ceremony to be led by USAID administrator Henrietta Fore.
Granville, 33, was shot and killed early Tuesday as he headed home from a New Year's party in Khartoum, his family has said. A U.S. Foreign Service diplomat from Buffalo, New York, he was working to restore peace in the war-torn nation. Watch I-Report video of shooting scene »
U.S. officials are working with Sudanese authorities to investigate the incident. The FBI said Wednesday it was sending a team to Sudan to assist investigators.
Granville's family has said there was no particular reason for him to be targeted, because the nature of his work was not political. See family photos of Granville's life »
"Here is the global infidelity harming the Nation of Islam with collaboration with the people of division and hypocrisy in order to push the people away from the path of God and to humiliate the men and violate the honor of the Muslim woman and violate the honors of Muslims in order to raise the banner of the cross above the land of Sudan, but the soldiers of monotheism swore to their God not to give in to this earthly life except their faith," Friday's statement began.
"We ask God to consider this act blessed to his generous being and we ask [the] almighty to please the hearts of the believers and please our Mujahedeen brethrens all over the lands of the Muslims," it said.
Earlier this week, a Sudanese Foreign Ministry spokesman said the shooting occurred during a "street argument."
Spokesman Ali As Sadeq said the streets of the city were packed with cars leaving a New Year's celebration, and a dispute broke out between people in two cars, one of which was carrying foreigners. The argument escalated, and a Sudanese fired on the car carrying the foreigners, he said.
Granville's family said he became passionate about Africa after helping build a school in a rural Cameroon village as a Peace Corps volunteer.
"John's life was a celebration of love, hope and peace," the family statement said. "He will be missed by many people throughout the world whose lives were touched and made better because of his care."
He is survived by his mother, sister, nephew and nieces.
Jane Granville said her son was aware of the dangers in the countries where he worked.
"I did discuss his safety all the time, and he said, 'Mom, I want you to listen to me. I am doing what I love every day of my life. How many people could ever say that? I get up, I go to work and I try to make a little difference, and I love what I'm doing.' So that was John's answer."
His mother said Granville got the "traveling bug" while in high school, and described him as a humanitarian who loved Africa and its people and believed he was a guest in Sudan.
"The least that I can be is strong, because that's what John would have wanted. He would have wanted us to celebrate his life, and that's what we're trying to do," Jane Granville said.
Sudan has been on the State Department's list of nations that sponsor terrorism since 1993, and the U.N. Security Council imposed sanctions on it from 1996 to 2001 because of its involvement with terrorism, according to the Council on Foreign Relations.
The country's government has provided sanctuary to terrorists including Osama bin Laden, the council said.
But in 2005, the State Department said Sudan's cooperation and information-sharing had increased and that it had made progress in combating terrorism, according to the council's Web site. E-mail to a friend
CNN's Marylynn Ryan, Tracy Doueiry and Charley Keyes contributed to this report.
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