ISIS claimed responsibility for the attack in Texas

Holly Yan- CNN

ISIS has claimed responsibility for the attack outside a Prophet Mohammed cartoon contest in Texas -- and warned of more attacks to come.

In a broadcast on its official radio channel Tuesday, the group said two Al Khilafa soldiers opened fire outside the event in Garland, a Dallas suburb. Al Khilafa is how ISIS refers to its soldiers.

CNN cannot confirm the claim, and ISIS offered no evidence that the gunmen were affiliates with the terror organization.

The gunmen, Elton Simpson and Nadir Soofi, wounded a security guard before police shot and killed them.

Nadir Soofi, left, and Elton Simpson were the two gunmen in the Garland, Texas, shooting.

The ISIS radio announcer also referred to Simpson and Soofi as the terror group's "brothers." The announcement ended with this warning:

"We say to the defenders of the cross, the U.S., that future attacks are going to be harsher and worse. The Islamic State soldiers will inflict harm on you with the grace of God. The future is just around the corner."

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