Following the mass shooting at a gay night club in Orlando, Fla. that killed 50 people and wounded 53 others, officials identified 29-year-old Omar Mateen as the shooter and began to investigate his possible connection to terrorist activity. Several news sources, including CNN, reported that Mateen pledged allegiance to ISIS in a 911 call he made during the attack. His association with the Islamist militant group was confirmed in a statement issued by ISIS' official radio station on Monday; the group claimed responsibility for the attack.

According to the New York Times, the radio statement included the following:

"With facilitation from Allah the Almighty, the brother Omar Mateen, one of the soldiers of the Caliphate in America, carried out a security raid in which he was able to enter into a gathering of Crusaders in a nightclub for followers of the people of Lot in Orlando, Florida. Allah enabled him to subdue the impure Crusaders, killing and wounding more than a hundred of them before he was killed — may Allah accept him. It should be pointed out that this invasion is the largest in America in terms of the number killed."

This announcement comes after the Amaq News Agency, the Islamic State's official media arm, made a similar statement on Sunday. Unlike the radio announcement, articles published on Amaq tend to use unbiased, neutral language in an attempt to appear objective, though the New York Times reports that analysts agree the agency is a mouthpiece for ISIS.

The Islamic State formally claims responsibility for the Orlando attack via @rcallimachi

— The New York Times (@nytimes) June 13, 2016

Mateen was previously been under investigation after he was suspected of having extremist ideology; in 2014, the FBI discovered that he had made contact with the first American suicide bomber in Syria. Mateen's specific ties to ISIS remain unclear, however, although ISIS has referred to him as a "solider of the Caliphate." ISIS uses the term "Caliphate" to describe the territory it controls, Business Insider reports