Latest: Four security officers were killed and five others were wounded when a suicide bomber detonated his vest outside one of Islam's holiest sites.

Two gunmen were killed after opening fire on a security officer outside a contest for cartoon depictions of Prophet Muhammad and a bomb squad was called in to search their vehicle as a precaution, authorities said.

FBI agents have searched an apartment in Phoenix as part of an investigation into a shooting outside a Dallas venue hosting a contest for Prophet Muhammad cartoons.