U.S. citizens should be extra cautious, maintain a very high level of vigilance, and take appropriate steps to enhance their personal security, the U.S. State Department said in a travel alert.
The alert, issued December 19, cited the lone wolf attack in Sydney, Australia, on December 15, 2014, resulting in the deaths of two hostages.
"An analysis of past attacks and threat reporting strongly suggests a focus by terrorists not only on the targeting of U.S. government facilities but also on hotels, shopping areas, places of worship, and schools, among other targets, during or coinciding with this holiday period," the alert said.
"U.S. citizens abroad should be mindful that terrorist groups and those inspired by them can pose unpredictable threats in public venues. U.S. citizens should remain alert to local conditions and for signs of danger," according to State.
State recommends that U.S. citizens traveling abroad enroll in the Department of State's Smart Traveler Enrollment Program (STEP).