An Islamist militant who blew himself up while fighting government troops in northern Syria is believed to be the first US national to carry out a suicide attack in the country since the civil war started in 2011.
US officials confirmed claims by Jabhat al-Nusra - an al-Qaida affiliated rebel group - that one of four suicide bombers who died in an attack in Idlib province was an American citizen.
Twitter messages from al-Nusra identified the man only by his Arabic nom de guerre: Abu Hurayra al-Amriki.
The messages were accompanied by a photo depicting a smiling, bearded man holding a kitten.
American officials speaking on the condition of anonymity told NBC news that they believed the man was a US national but refused to provide his true identity or hometown.
The same man was shown wearing a suicide vest, while posing with three other jihadists, in another photo released by extremist websites.
The Syrian Observatory for Human Rights reported that four suicide bombers from al-Nusra detonated as many booby trapped cars against regime's checkpoints near the city of Ariha, in Idlib province, at the end of last week.
According to official estimates, hundreds of western citizens have joined fighting in Syria.
The FBI said that among them are several dozens of Americans, but none was known to have carried out a suicide attack before.
In February, a jihadist nicknamed Abu Suleiman al-Britani reportedly blew himself up in an attack against a prison in Aleppo, becoming the first British suicide bomber in the war.