“In Switzerland, the terrorist threat remains at a heightened level,” the FIS said in its annual assessment of risks faced by Switzerland.
“The most likely terrorist threat in Europe and thus also in Switzerland will continue to come from jihad-motivated terrorism,” it said. “Further attacks must be expected.”
The assessment was released as Europe still comes to terms with attacks in London and Paris linked to Islamist extremism.
The FIS said the greatest danger was that individuals or small groups inspired by Islamic State would carry out attacks in Switzerland or use it as a base to plot other attacks.
FIS said it had identified more than 500 internet users with Swiss connections who were using social media to spread jihadist ideas.
Concerns about extremism and potential attacks led to Swiss voters last year backing a law extending the national spy service’s authority to monitor internet traffic, deploy drones and hack foreign computer systems.
Switzerland has so far not been targeted directly in an Islamist attack, but it has had several links to attacks that occurred elsewhere in Europe last year.
Two men who took hostages and killed a priest in northern France last July had traveled via airports in Geneva and Zurich.
Another man who killed at least 12 people when he drove a lorry into a crowded Berlin market had also visited Switzerland and may also have obtained a gun there.
“It is not yet clear whether these links to Switzerland played any role in the attack,” the FIS report said.
With no indication the fight against Islamic State was coming to a close, there “remains the considerable risk that the aggressive battle for the survival of the caliphate, fought using every means at their disposal, will increasingly be carried to Europe,” the FIS report said.
Radicalized individuals returning from war zones were the most likely perpetrators, although the number of people leaving Switzerland to fight in Syria and Iraq had declined.