An American citizen carried out a suicide bombing in Syria on behalf of an Al-Qaeda-linked terrorist group on Sunday, the first time a U.S. citizen has carried out such an attack in the Syrian civil war, NBC News reported on Wednesday.

Law enforcement and counterterrorism officials who spoke to NBC on condition of anonymity, confirmed the suicide bombing and said they have identified the American. They declined to release his identity or hometown.

Word of the American’s death in the suicide bombing first surfaced Tuesday in tweets from the Al-Nusra Front, an Al-Qaeda-linked group fighting the government of Syrian President Bashar Al-Assad.

The head of Al-Nusra Front has pledged allegiance to Al-Qaeda chief Ayman al-Zawahiri, and the group has been blacklisted as a terrorist organization by both the U.S. and the United Nations.

According to NBC, the tweets identified the bomber only by his Arabic nom de guerre, “Abu Hurayra al-Amriki,” (Abu Hurayra the American) and said he carried out one of four suicide bombings of Syrian government sites in Jabal al-Arbaa’in in Idlib Province, the scene of heavy fighting in recent weeks and months.

The tweet included an image of a young, bearded and smiling Caucasian man holding a cat, as well as images of the bombing it said he had carried out. Another tweet, this one in Arabic, included a photo showing the same light-skinned man sitting on the ground wearing what appeared to be a suicide vest.

Separately, a video circulating on jihadi forums showed what appears to be the same man loading artillery shells into a truck bomb and then the bomb exploding in the city.

Syrian rebel sources based in London told NBC News that other jihadi tweets suggest the American was of Palestinian Arab descent.

The incident is believed to be the first suicide bombing by a U.S. citizen in the Syrian civil war. Three Americans were confirmed to have carried suicide attacks in Somalia on behalf of another Al-Qaeda linked group, Al-Shabaab, between 2009 and 2011.

Foreign fighters entering Syria and fighting alongside the rebels has been a great concern for several countries.

In February it was estimated that at least 50 U.S. citizens are fighting in Syria against Assad, and are liable to bring terrorism back to their home country once the war is over.

Other published statistics say that over 75,000 foreign nationals have been fighting in the Syrian civil war. While the majority are from Muslim countries, there are also Russians, Germans, Canadians and French citizens taking part in the fighting.