In a message broadcast by Isis’s official radio station based in Mosul, Iraq, the group called the shooters at the event in Garland “two soldiers of the caliphate”.
Authorities in Texas have identified the two attackers as Elton Simpson and his roommate Nadir Soofi, both from Phoenix in Arizona. They opened fire on an exhibition organised by the anti-Muslim American Freedom Defense Initiative (AFDI), wounding a security guard, and were shot dead by police.
Social media accounts linked to Isis had previously hailed the actions of the shooters, but the message issued by Idha'at al-Bayan is the first time an official media outlet for the group has claimed responsibility for an attack on US soil.
Texas shooting in pictures
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"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 broadcast said.
Texas police have now confirmed that SWAT team officers were involved in returning fire against the two gunmen.
Garland police spokesman Joe Harn said that after the men pulled up in a car and opened fire, a single police officer subdued them both, but that after his initial shots SWAT officers also fired at the two men. Harn said police don't know who fired the lethal shots.
There was a strong police presence at the controversial event, and police have said they "expected" some sort of incident. Harn said the two gunmen were stopped some distance from the entrance to the Curtis Culwell Center, where attendees were about to leave the event that had offered a $10,000 prize for the "best" cartoon of the Prophet Mohamed.
Depicting Mohamed is seen as highly offensive to Muslims, yet event organiser and AFDI founder Pamela Geller has denied deliberately seeking to be provocative or accusations of Islamophobia.
She told CNN the shooting "shows the need for such conferences", and said the cartoon display was "very well received". "The winner was a former Muslim," she added.
The US's largest Muslim advocacy organisation condemned the attack on Monday. It said that there was never an excuse for violence in response to "bigoted speech", and said that incidents like the one in Garland were "more insulting to our faith than any cartoon".
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