A U.S. diplomat in Riyadh declined to say if the upgrade was in response to a specific terrorist threat.
The Riyadh Diplomatic Quarter, a large residential area east of the city, has been heavily guarded by Saudi armed forces since the May 12 suicide attacks on foreign housing compounds. Those attacks killed 35 people, including the nine assailants. Another 17 people were killed in a Nov. 8 suicide attack on another compound.