Americans have been warned to be alert to possible travel risks, especially during the holidays, following increased terrorist threats around the world.

US issues holiday travel warning.

US issues holiday travel warning. Image by Dave Hosford / CC BY 2.0

The State Department issued a travel alert, which will be in effect until February 24, saying current information suggests that militants with the Islamic State, al-Qaida, Boko Haram and other terrorist groups continue to plan attacks in multiple regions.

The US authorities said the likelihood of terror attacks will continue as members of IS return from Syria and Iraq, and other individuals not affiliated with terror groups engage in violence on their own.

Extremists have targeted sporting events, theatres, open markets, cafes and restaurants and aviation.

In the past year, there have been multiple attacks in France, Nigeria, Denmark, Lebanon, Turkey and Mali.

IS has claimed responsibility for the October 31 bombing of a Russian airliner in Egypt, killing 224 people.

“US 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 US is exchanging information with allies about threats of international terrorism.

The travel alert was issued the 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 November 13 attacks in Paris that killed 130 people have virtually shut down the Belgian capital.

(Press Association)