The Islamic State group has claimed responsibility for Sunday's shooting attack on an art exhibit in Garland, Texas, which showed depictions of the Prophet Muhammad.

In a statement on the group’s Al Bayan radio station, ISIS confirmed that “two soldiers of the caliphate” were responsible for the attack, the Associated Press reported. It did not provide further details and the report speculated whether ISIS may have opportunistically claimed an independent attack.

Elton Simpson and Nadir Soofi, two roommates who opened fire on the center in the Dallas suburb of Garland, were killed by security forces on Sunday. Simpson had been investigated by the FBI for terrorism five years ago, and was convicted of lying to federal authorities about his plans to travel to Africa, BuzzFeed reported.

In the statement, ISIS reportedly said: "We tell America that what is coming is more bitter and harder and you will see from the soldiers of the Caliphate what harms you."