The travel alert is expected to expire by the end of January 2018.
The US has issued a travel alert for Europe, warning its citizens of the "heightened risk of terrorist attacks" throughout the region.
Citing recent widely-reported incidents in multiple European countries, including France, Britain, and Sweden, the State Department on Thursday said it remained concerned about potential future terrorist attacks, reports Xinhua news agency.
The incidents demonstrate that the Islamic State, Al Qaeda, and their affiliates were still capable of planning and executing terrorist attacks in Europe, the Department said in a statement.
It also warned of self-radicalised extremists who may conduct attacks "with little or no warning".
The US will continue to work closely with its European allies to tackle terrorism, it noted.
The travel alert is expected to expire by the end of January 2018.