The US State Department on Friday confirmed that an American citizen had carried out a suicide bombing in Syria.
A US security official identified the dead American as Moner Mohammad Abusalha.
The New York Times, which first reported his name, said he grew up in Florida and traveled to Syria last year.
The official said US agencies were aware before the suicide bombing that the American had traveled to Syria to join militants, although the official declined to offer further details.
The official said that unlike some other foreign fighters in Syria, the American suicide bomber was not known to have posted messages on Twitter or other social media websites.
The bomber, who used the nom-de-guerre 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.
"I can confirm this individual was a U. citizen involved in a suicide bombing in Syria," State Department spokeswoman Jen Psaki said at a news briefing.