Confirming the news to paper Le Tribune de Genève, a spokesman for the Swiss public prosecutor’s office said a 29-year-old with dual Swiss-Tunisian nationality was arrested on his return from Turkey on August 9th.
According to the paper, police suspected the practising Muslim had been radicalized.
After he took a plane to Istanbul last October, his mother told the paper she thought the police feared he was travelling on to Syria.
In February the public prosecutor opened a case against him and a 21-year-old friend, who was arrested in June.
The pair are suspected of breaking the Swiss law which bans terror groups Al-Qaeda and Isis.
They are accused of supporting and participating in criminal organizations, the Swiss public prosecutor’s office told the paper.
“These arrests illustrate the rigorous procedures against anyone in Switzerland suspected of trying to participate in terrorism as part of the jihadist movement,” said the spokesman.
In July a Swiss court made history when it convicted a man for attempting to travel to Syria to join Isis, the first time anyone had been prosecuted for such an act.
The Swiss-Lebanese man was arrested at Zurich airport before getting on a flight to Istanbul in 2015 “with a view to joining Isis and dying as a martyr”, judged the court.
In June the government asked the justice department to draw up a proposal to stop alleged Swiss jihadists travelling overseas to fight, potentially by stripping them of their travel documents.