The department did not advise people against travel but said US citizens should be vigilant, especially in crowded places. The State Department has regularly issued such worldwide travel alerts since the September 11, 2001, attacks on the United States. A State Department official said the latest alert, which expires February 24, effectively updated past warnings.

In the statement on its website, the State Department said: "Current information suggests that (Islamic State), al-Qaeda, Boko Haram, and other terrorist groups continue to plan terrorist attacks in multiple regions."

Although it did not mention the November 13 Paris attacks claimed by the Islamic State group in which 130 died, the department noted that militants had carried out attacks in France, Nigeria, Denmark, Turkey, and Mali during the past year.

France and Belgium have launched a manhunt following the attacks in Paris, with a focus on Brussels barkeeper Salah Abdeslam, 26, who returned to the city from Paris hours after the attacks and is still at large.

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