The office issued a statement late Thursday stating that federal authorities were working closely with Geneva cantonal police and judicial authorities who are reportedly seeking at least four and possibly six people suspected of planning an attack.

“The ultimate goal is to prevent a terrorist event,” the federal prosecutor’s office said.

It said federal authorities transmitted information on Wednesday information about the “possible planning of a terrorist event” to Geneva security officials.

The federal prosecutor’s office opened a criminal case against “persons unknown” on suspicion of membership in and support of an organization such as Al Qaeda or Islamic State (Isis) that is outlawed in Switzerland.

Various newspapers in the Lake Geneva region have published a photo of four bearded men, with their faces blanked out, who are purportedly being sought by police.

Le Matin newspaper said the photo was transmitted by American authorities.

It shows the men raising their forefingers in the air in the manner of Isis combatants.

According to a document that Le Matin said it had seen, the individuals being sought by police are “armed and dangerous”.

AFP also reported that police in the two French regions bordering Geneva — Ain and Haute-Savoie — told the news agency that controls had been beefed up at all crossings.
   
“The police, the gendarmes and the customs officers are on the ground and are reinforcing their inspections,” said a police spokesman in Ain, with similar comments from an official in Haute-Savoie.
   
Meanwhile, in France, a man was detained Thursday after weapons were discovered in his home in a continuation of the rolling searches seen since a state of emergency was imposed after the bloodshed in Paris.
   
Officials in the Drôme region said the suspect was found during a traffic stop in possession of a picture of Salah Abdeslam, the key Paris suspect who remains at-large.
   
The individual was reportedly known to police in the area over previous incidents of low-level criminality.
   
Switzerland said last month that it had active criminal proceedings against 33 individuals over suspected ties to extremist Islamist groups, but only three people were in custody.
   
The most serious case involves a cell of possible Islamist radicals uncovered in the canton of Schaffhausen, near the German border, last year.