By Mark Hosenball
WASHINGTON, May 28 (Reuters) - U.S. government agencies were examining social media postings purporting to show how an American who was fighting with an Al Qaeda affiliate blew himself up recently in a suicide attack in northern Syria, U.S. officials said.
The officials, who declined to be identified, said U.S. agencies assessed that the postings were likely authentic. One said some investigators believed they knew the "U.S. person's" true identity, but declined to give further details.
According to internet postings, the suicide bomber, who called himself "Abu Hurayra al-Amriki" carried out one of four suicide bombings on May 25 in Syria's Idlib province on behalf of Jabhat al-Nusra, al Qaeda's affiliate fighting to oust the government of President Bashar al Assad.
If his identity is confirmed, he would be the first American known to have committed a suicide bombing in Syria on behalf of al Qaeda, said Laith Alkhouri, a senior analyst with Flashpoint Global Partners, which monitors militant websites for government and private clients.
Alkhouri said social media postings, including Twitter messages and a video posted on YouTube, showed Abu Hurayra posing in a still picture with three other suicide bombers, one of whom was Syrian. The other two were foreigners.
The video shows a truck-sized vehicle being loaded with explosives and then cuts to a long-shot of a fortress-like structure on top of a hill being blown up.
Shiraz Maher, a researcher with a University of London think tank, said that last week, an al Qaeda media outlet issued a short promotional video about a forthcoming film related to an "American" fighter in Syria.
The teaser, which opens with a graphic of a burning American flag and an exhortation to "Join the Caravan of Jihad and Martyrdom," promotes a longer video featuring "The story of an American Muhajir (visitor) in Sham (Syria)."
The short video includes a brief sound bite in which a man with an American or Canadian accent, whose face is blurred, declares: "It is huq (right) on you to fight."
Maher, whose think tank has studied the role of social media in recruiting foreigners to join militant groups in Syria, said he had spoken to a British fighter in Syria who confirmed the suicide bomber was American and described him as "a beautiful brother."
One Twitter message included a picture of a man identified as Abu Hurayra holding a kitten, as well as pictures of the booby-trapped truck and an explosion.
Two officials said the FBI and Justice Department were aware of the case.
(Editing by David Story and Bernadette Baum)