A US citizen who was fighting in Syria with the nom de guerre Abu Hurayra al-Amriki — or Abu Hurayra "the American" — died in a suicide attack in Syria's Idlib province last Sunday, according to rebel sources.

News of the American's "martyrdom" was spread over social media by fellow fighters and is under investigation by US authorities. Two unnamed US officials told Reuters that the reports are likely "authentic" — with one suggesting investigators might know the man's identity.

If reports are confirmed, al-Amriki would be the first known US citizen to have died in a suicide operation in Syria — where suicide attacks by foreign fighters, including those from Western countries, are not unusual.

"Almost 90 percent of suicide operations are done by foreigners, not Syrians! Syrians are not that radical, comparing with those who came from the other countries," Ahmad Beetar, a Syrian independent blogger who documented the conflict from Syria before fleeing in August 2013, told VICE News. "All radical Muslims are receiving the same information and are being brain-washed the same way. There is the Internet, videos and Jihadi websites: anyone can be recruited if he is able to be brain-washed."

The American, who was fighting against Syrian government forces with the al Qaeda affiliate Jabhat al-Nusra, reportedly died in one of four suicide bombings carried out by the group over the weekend.

In the photo below, the American is seen posing with three other suicide bombers, only one of whom was Syrian. Rebels also shared video of the fighters preparing the attack.

Pic shows American suicide bomber, Abu Hurayrah, with another bomber, Abu Turab from the Maldives, in — Charles Lister (@Charles_Lister)May 29, 2014

The videos below, shared by rebel sources and local activists, show two explosions reportedly carried out by suicide bombers, in a series of operations to capture government-controlled checkpoints near Ariha and Khan Sheikhoun, in Idlib province. Al-Amriki is believed to have carried out one of the attacks, though VICE News cannot independently verify that.

The British-based Syrian Observatory for Human Rights confirmed that four attacks took place.

Shiraz Maher, a researcher at the International Centre for the Study of Radicalization (ICSR), said that an al Qaeda-linked media outlet recently released a promotional video about an American fighter in Syria, according to Reuters.

The video, re-uploaded below, opens with the burning of an American flag and an exhortation to "Join the Caravan of Jihad and Martyrdom," and includes a brief soundbite in which a man with an unidentifiable American accent says, "It is huq (right) on you to fight."

Maher also told Reuters that he spoke to a British fighter in Syria who confirmed the suicide bomber was American and described him as "a beautiful brother."

The ICSR reported in December 2013 that up to 60 US citizens were estimated to have traveled to Syria to fight alongside rebels there.

Fellow rebels also posted a series of social media tributes to the American and the other foreign "martyrs" killed in the operation.