Amaq News, a Syrian news agency with close ties to the Islamic State, says the group is responsible for the attack on an Orlando gay club, which has killed 50 people, and left 53 injured.

“The armed attack that targeted a gay night club in the city of Orlando in the American state of Florida which left over 100 people dead or injured was carried out by an Islamic State fighter,” Amaq said.

The shooting, which took place in the early hours of Sunday, was carried out by Omar Mateen, a 29-year-old Muslim US citizen, who was brought up by a family of first-generation Afghan immigrants.

Earlier, Mateen’s father, Mir Seddique, claimed the incident had “nothing to do with religion,” and speculated that it was caused by his son’s dislike of public displays of homosexuality.

But US security sources told various news outlets that Mateen had been investigated in 2013, and 2014, over alleged social media threats, but that no charges had been brought forward, due to lack of evidence.

FBI officials on the scene also said they suspected Mateen of “radical leanings” but did not rule out any explanation for the murder spree at this point.