The State Department issued a worldwide travel alert Monday over possible risks due to increased terrorism threats.

The alert comes amid information that ISIS, Al Qaeda, Boko Haram, and other terrorist groups continue to plan attacks in multiple regions by employing a “wide variety of tactics,” according to the State Department.

Authorities believe the likelihood of terror attacks will continue as members of ISIS return from Iraq and Syria, as well as the threat from “unaffiliated persons” planning attacks inspired by major terrorist organizations.

The State Department said that U.S. citizens should “exercise vigilance when in public places or using transportation” and “avoid large crowds or crowded places.”

Americans  are also urged to exercise particular caution during the holiday season, and at holiday festivals or events. The worldwide travel alert expires on Feb. 24, 2016.

The alert was issued after multiple attacks in the past year in France, Nigeria, Denmark, Turkey and Mali in the past year, as well as the bombing of a Russian airliner in Egypt, for which ISIS has claimed responsibility.

The State Department said that U.S. citizens should factor updated information into personal travel plans, and urges anyone with specific safety concerns to contact local law enforcement authorities.

A State Department official told Fox News that worldwide alerts “are issued periodically when there is a higher threat level," and are not the same as a warning tied to a particular event, like an election or hurricane.

“We want folks to still travel, but just to exercise greater vigilance,” the official said.

But despite the label “worldwide,” the alerts do not cover the territory of the United States itself.

The State Department said the U.S. is exchanging information with allies about threats of international terrorism.

The travel alert was issued the same day that Belgium's prime minister announced that Brussels would remain at the highest alert level for at least another week.

The increased security measures following the Nov. 13 attacks in Paris that killed 130 people have virtually shut down the Belgian capital.

There have been a total of six worldwide travel alerts in the last four-and-a-half years.

Fox News' James Rosen and The Associated Press contributed to this report.