ISIS Claims Responsibility for Muhammad Cartoon 'Contest' Shooting

Updated: May 05, 2015 8:58 AM ET

The Islamic State of Iraq and Greater Syria (ISIS) has claimed responsibility for the Sunday shooting outside a controversial cartoon competition that lampooned the Prophet Muhammad near Dallas that left the two assailants dead — the first time the group has claimed an attack on U.S. soil.

A statement read on the extremist group's Al Bayan radio Tuesday said that "two of the soldiers of the caliphate" executed the attack in Garland, Texas, Agence France-Presse reports.

"We tell America that what is coming will be even bigger and more bitter, and that you will see the soldiers of ISIS do terrible things," the group said.

Reports emerged Monday that the FBI had been investigating one of the shooters, Elton Simpson, since 2006 after it found recordings of the 31-year-old vowing to "fight nonbelievers for Allah."

While there has been no acknowledged link between Simpson, fellow gunman Nadir Soofi, 34, and ISIS, Reuters reported that the FBI had been investigating whether the attack had been instigated by foreign-based militants.

The cartoon contest has been deemed deliberately provocative, as any depiction of the Prophet Muhammad is forbidden in Islam.

All products and services featured are based solely on editorial selection. TIME may receive compensation for some links to products and services on this website.