"Authorities believe the likelihood of terror attacks in Europe will continue as European members of ISIL [Islamic State] (Daesh) return from Syria and Iraq," the bureau stated.
"Additionally, there is a continuing threat in Europe from unaffiliated persons planning attacks inspired by major terrorist organizations but conducted on an individual basis."
On Thursday night, a truck rammed into a large crowd that was celebrating Bastille Day in Nice. At least 84 people, including children, were killed and dozens of others were injured.
The driver was shot dead by police. According to identification documents found inside the truck, the driver was a 31-year-old male resident of Nice of Tunisian origin. It is unclear whether he had any accomplices.
The US authorities advised Americans to avoid large crowds in France, which may increase the risk of a terror attack, and urged them to exercise vigilance.
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