Two Syrian men have now been arrested after traces of explosives were found in their car.
The pair were detained in Geneva area after their suspicious behavior raised concerns.
Traces of explosives were found in their French-registered grey Renault Scenic, say police.
Officers closed the road, which links Thonon-Les-Bains and Cologny – one of Switzerland’s most affluent towns – for almost three hours after Friday’s incident.
The men, who have valid Syrian passports, deny the charges and maintain they only recently acquired the car.
At a hastily convened press conference last night, Geneva Attorney General Olivier Jornot refused to elaborate on the reason why the suspects’ came to the attention of officers.
Mr Jornot said that ‘arrests will multiply’ over the coming days, but he added that this would be due to the heightened checks and did not mean they would all be linked to international terrorism.
One of the two occupants was reported to be an acquaintance of Salah Abdeslam, the man wanted in connection with the deadly Paris terror attacks last month.
In a separate development, Swiss authorities said they had been tipped off by the CIA about a suspected IS cell in the region.
A photograph of four suspects has been circulated to police, but officials said last night there was no connection between the wanted men and the two Syrians arrested on Friday.
Read More: Switzerland arrests two Syrians on suspicion of terror links
