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The US State Department has issued a rare global travel alert for possible travel risks due to 鈥渋ncreased terrorist threats.鈥澛�

While there is no specific threat in the United States, the department warned that people should be more聽vigilant聽after recent multiple attacks in France, Nigeria, Denmark, Turkey, and Mali.

In a message posted 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."

Noting that extremists have targeted 鈥渓arge sporting events, theatres, open markets, and aviation services,鈥� the travel alert tells travelers to 鈥渆xercise vigilance鈥� while in public and 鈥渁void large crowds or crowded places. Exercise particular caution during the holiday season and at holiday festivals or events."

While the government has regularly issued individual country travel alerts since the Sept. 11, 2001, attacks, worldwide alerts are rare.

"Authorities believe the likelihood of terror attacks will continue as members of [Islamic State] return from Syria and Iraq," it said. "Additionally, there is a continuing threat from unaffiliated persons planning attacks inspired by major terrorist organizations but conducted on an individual basis."

The warning comes as the world grapples with the Nov. 13 terror attacks in Paris that killed 130 people and injured hundreds and a hotel siege in Mali in which 19 people died.

Meanwhile, Belgium鈥檚 capital Brussels spent much of the last few days in lockdown over fears of militant attacks.

The travel alert will remain in place until Feb. 24, 2016.

The advisory comes just as America's busiest travel week of the year gets under way. Airlines for America (A4A), a trade group for the airline industry projects that around聽25.3 million expected to fly聽during the Thanksgiving holiday, the highest level since the 2008 economic downturn.

The full alert follows:

This report contains material from the Associated Press.