The warning comes days after French counterterrorist police seized a haul of weapons and arrested seven people, taking orders from Syria, thought to have been plotting to hit Christmas events.
With a “focus on the upcoming holiday season and associated events”, the State Department in Washington D.C. said organised attacks, such as those in Paris last November and in Brussels in March, as well as lone-wolf attacks, were possible.
“U.S. citizens should also be alert to the possibility that extremist sympathizers or self-radicalized extremists may conduct attacks during this period with little or no warning,” they said.
The jihadists could use “non-conventional weapons and target both official and private interests”, they claim, continuing: “U.S. citizens should exercise vigilance when attending large holiday events, visiting tourist sites, using public transportation, and frequenting places of worship, restaurants, hotels, etc.
“Be aware of immediate surroundings and avoid large crowds, when possible.”
The terror suspects apprehended in France were of French, Moroccan, and Afghan origins and are thought to have been planning their attacks in Strasbourg and Marseille, whilst taking orders from Syria, Le Parisien reports.
Four men were apprehended in Strasbourg over the weekend, and police recovered four handguns and a submachine gun during house searches. Several mobile phones, SIM cards, encrypted messaging software, and jihadist propaganda were also found.
One of the men, named as B. Yassin, 37, a civil servant in a local primary school, is believed to have travelled to Syria via Cyprus in 2015.
In Marseille, three men were detained, who had already been reported to the authorities as “radicalised”.
Following Monday’s arrests, Patrick Calvar, the director general of France’s internal security operations, warned of a “dark period” during which “our enemies will stop at nothing to try to terrorise us”.
He added: “The level of the threat is such that we cannot rest on our laurels… There is no need to hide it: the challenge is immense, and we still have to redouble vigilance.”