GENEVA—Police in Switzerland’s capital evacuated Parliament and related offices Tuesday after a man in a bulletproof vest was arrested near one of its entrances and found to be bearing explosives.

Berne police said in a statement that in the early afternoon, “federal security staffers noticed a man at the southern entrance of the Parliament building whose appearance—he was wearing a bulletproof vest and weapon holster—and behavior were suspicious.”

“During a body check that followed, a rapid test turned up explosives,” the statement said.

The statement did not provide any detail on the explosives.

The suspect, who was not identified, was undergoing physical and mental exams, the statement said. Federal prosecutors and police opened a criminal investigation. There was no immediate indication about a possible motive.

Police cordoned off Federal Square outside the ornate parliament building and nearby streets for several hours as they dispatched security teams—including fire squads and de-mining experts, backed by a police dog and drones—to inspect an abandoned car that had been associated with the suspect.

Security measures were lifted after it turned out that the vehicle presented no danger, the police statement said.