The US Department of State on Sunday advised Americans worldwide, and especially in the Middle East, to exercise increased caution.

"Diplomatic facilities, including outside the Middle East, have been targeted. Groups supportive of Iran may target other US interests overseas or locations associated with the United States and/or Americans throughout the world," said the notice.

The statement also warned that "periodic airspace closures may cause travel disruptions" and "Americans abroad should follow the guidance in security alerts issued by the nearest US embassy or consulate."