Following the beheading of American journalist James Foley by ISIS, one Marine is issuing his own warning to the terror group.

Iraq war veteran Nick Powers wrote on Facebook, “Remember we are armed in the U.S. and I can promise you this … You attack us and there will be no mercy.”

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ISIS claims that the killing was in retaliation against U.S. airstrikes against the militants in Iraq. At a press conference on Thursday, Defense Secretary Chuck Hagel called ISIS “beyond anything we’ve seen.” He said the U.S. is “looking at all options.”

Army General Martin Dempsey, chairman of the Joint Chiefs of Staff, added that the group can be contained but cannot be defeated without attacking it in Syria.

This morning on Fox and Friends, Powers said there is no way to defeat ISIS without boots on the ground.

“You can bomb whatever you want, but without boots on the ground, you’re never going to fully accomplish any kind of mission militarily.”

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