Americans planning to travel this holiday season should remain vigilant.

The State Department issued a worldwide travel alert on Monday, advising United States citizens of “increased terrorist threats.” The alert is effective through Feb. 24, 2016.

The State Department’s website posting does not mention a specific new threat, but noted terrorist groups Al-Qaida, the Islamic State, Boko Haram and others are continuing to plan attacks.

“These attacks may employ a wide variety of tactics, using conventional and non-conventional weapons and targeting both official and private interests,” the department wrote.

The State Department also warned of a “continuing threat” from individuals who are not affiliated with a terrorist organization, but might have been inspired by a group’s attacks.

It pointed to recent plots on sporting events, theaters and airliners, and said authorities think terrorist attacks are likely to continue as members of the Islamic State come back from Syria and Iraq.

The alert encourages travelers to remain alert, be aware of their surroundings and avoid large crowds.

“Exercise particular caution during the holiday season and at holiday festivals or events,” the State Department warned.

According to its website, such travel warnings are issued when the State Department wants individuals “to consider very carefully whether (they) should go to a country at all.”