Americans should be on alert to possible travel risks, especially during the holidays, following "increased terrorist threats" around the world, the U.S. State Department warned in a press release Monday.

The travel alert, which is in effect until Feb. 24, said current information suggests that militants with ISIS, al-Qaeda, Boko Haram and other militant groups continue to plan attacks in several regions around the world. U.S. authorities said the likelihood of attacks will continue as members of ISIS return from fighting in Syria and Iraq to their home countries and lone-wolf actors perpetrate acts of violence on their own.

The release said extremists have targeted sporting events, theatres, open markets and aviation targets, and pointed to attacks in France, Nigeria, Denmark, Lebanon, Turkey and Mali in the past year. ISIS has claimed responsibility for the Oct. 31 bombing of a Russian airliner in Egypt that killed 224 people.

"U.S. citizens should exercise vigilance when in public places or using transportation," the alert said. "Be aware of immediate surroundings and avoid large crowds or crowded places. Exercise particular caution during the holiday season and at holiday festivals or events."

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.

Canada's Department of Foreign Affairs, Trade and Development has not issued a similar blanket travel alert. A spokesperson for the department told CBC News that Canadians can consult the government's list of country-specific travel advisories.

The list advises against all travel to Mali in light of the recent attacks in Bamako. It also encourages Canadians to exercise a high degree of caution in France. 

With files from CBC News