US officials are warning that a "maritime threat'' has been reported in the Red Sea off of Yemen.

The alert that went out early Saturday did not specify what the threat was. However, it comes amid heightened tensions between Iran and the U.S.

The alert from the U.S. Transportation Department's Maritime Administration read: "A maritime threat has been reported in the Red Sea in the vicinity of Yemen. The nature of the event is potential increased hostilities that threaten maritime security.''

The U.S. Navy's Bahrain-based 5th Fleet and the U.S. military's Central Command did not immediately respond to a request for comment Saturday.

The capital and areas of war-torn Yemen remain held by the country's Houthi rebels, which are allied to Iran. Shipping in the Red Sea has been targeted previously by rebel attacks.