The alert references outdoor markets, popular throughout the continent during the Christmas season, as potential terrorist targets.

Last week, the U.S. State Department issued a Travel Alert for Europe, citing holiday attacks last year on a Berlin Christmas market in early December and a nightclub in Istanbul on New Year’s Eve, both claimed by ISIS. The alert, which is effective immediately and expires on January 31, 2018, also references more recent terrorist attacks in Paris, St. Petersburg, Stockholm, London, and Barcelona, but warns that travelers should take precautions throughout Europe.

The advisory specifically asks American citizens to “exercise additional vigilance” when visiting popular tourist sites, outdoor Christmas markets that fill city squares across the continent, and when taking public transportation—three potential terrorist targets. The Travel Alert also makes reference to the efforts being carried out by authorities on the ground to prevent attacks: “local governments continue counterterrorism operations,” it reads. “We continue to work closely with our European partners and allies on the threat from international terrorism.”

The alert is the second issued for Europe around the holidays in two years, and last year’s echoed nearly the exact same reasoning and safety information. A similar continent-wide one was extended this past summer, in response to many of the same terror attacks mentioned in the holiday alert. It was set to expire on November 30.

The U.S. State Department issues Travel Alerts around specific events—in this case Christmas and New Year’s celebrations—as opposed to Travel Warnings, which are issued for ongoing threats such as those caused by civil wars or long-term political instability.