An Oklahoma sheriff is urging residents to arm themselves for a fight against radical Islam.

Carter County Sheriff Milton Anthony said in a letter posted to Facebook that "the times are changing and we live in a more violent world," citing the recent terrorist attack in San Bernardino, Calif.

"It may come a time that you as citizens may be called upon to defend the citizens of this country against all enemies foreign and domestic that want to do us harm or kill us," Anthony wrote. "By no means do I want to scare anyone, but the attacks are real."