The United States has issued a rare worldwide travel alert warning its citizens of "increased terrorist threats" following the November 13 Paris attacks, claimed by Islamic State (IS) militants, that left 130 people dead.
The U.S. State Department said in the November 23 warning that "current information suggests" IS militants, Al-Qaeda, Boko Haram, "and other terrorist groups continue to plan terrorist attacks in multiple regions."
The advisory cited recent attacks in Denmark, France, Mali, Nigeria, and Turkey.
"U.S. citizens should exercise vigilance when in public places or using transportation," the State Department said.
It advised Americans to avoid crowded places and "exercise particular caution during the holiday season."
"Extremists have targeted large sporting events, theaters, open markets, and aviation services," the alert said.
New "attacks may employ a wide variety of tactics, using conventional and non-conventional weapons and targeting both official and private interests," the State Department added.
The State Department regularly issues travel warnings for individual countries, but such worldwide alerts are unusual.
The advisory, which expires on February 24, warned travelers that "the likelihood of terror attacks will continue as" foreign fighters who have fought alongside IS militants in Syria and Iraq return home.
It also warned that individuals inspired by -- but not affiliated with -- terrorist groups could carry out "lone wolf" attacks.
Authorities in Belgium and France are continuing a massive manhunt for Belgian-born fugitive Salah Abdeslam, who is suspected of participating in the deadly Paris attacks, which have heightened security concerns across Europe.
Police in the German city of Hannover last week said that authorities canceled a friendly soccer match between Germany and the Netherlands because they had "concrete information" about a bomb threat.
Top government officials, including Chancellor Angela Merkel, had planned to attend the match to send a signal that Germany would not bow to terrorism following the gun and bomb attacks in Paris.
During the deadly coordinated assaults in French capital, Germany was playing France in a soccer friendly in the Stade de France, outside of which three suicide bombers blew themselves up, killing one bystander.