The three-month long warning reflects the increasing concern for the radical terrorism in the wake of the attacks in Paris in Nov. 13 and others in Beirut and the Sinai Peninsula that claimed some 400 lives.
"The current intelligence suggests that the ISIL, Al Qaeda, Boko Haram and other terrorist groups continue planning attacks in several regions," said the State Department.
They can use broad ranging tactics, conventional and non-conventional weapons in those attacks and aim them at both official and private interests.
The government warned of the possibility that terrorists could use "lone wolves" in the attacks, that is people inspired in an extremist organization but not directly controlled by them.
The alert urges citizens to be especially cautious during the holiday season and at holiday festivals or events.
Concerns about the extremists intensified in the past few weeks in the wake of the attacks in France, considered the prelude to more actions by the terrorist groups against Western targets.
The warning, to be in force until Feb.2, points to fears that ISIL fighters that are back in Syria and Iraq, and other individuals unafilliated with any specific group may perpetrate terrorist acts on their own.
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