Geneva (AFP) - Swiss authorities on Saturday said two Syrians had been arrested in Geneva after traces of explosives were found in their car, as police continued to hunt for several suspected jihadists with links to the Islamic State group.

Geneva prosecutor Olivier Jornot told a news conference that the two men had Syrian passports and only "recently arrived" in Switzerland. They spoke Arabic, he added.

They were arrested after police were alerted about "their behaviour".

He sidestepped questions on whether the pair were on visas allowing them to circulate freely through the visa-free Schengen zone.

But Jornot said they were not among the four men being searched as suspected jihadists planning attacks following the Paris carnage on November 13 and whose photographs have been released by the police.

Jornot said the two arrested men said they had recently bought the car they were travelling in and clarified that it only bore traces of explosives and not toxic gases.

He said they were arrested on the day they arrived in Switzerland.

The federal prosecutor's office had said in a statement earlier Saturday that the two men were arrested on suspicion of the "manufacture, concealment and transport of explosives and toxic gases" and of violating Swiss law prohibiting "groups like Al-Qaeda, Islamic State and similar organisations".

Jornot later clarified that "the vehicle was at one point used to transport explosives" but that it did not necessarily mean it was the two suspects who did so.

The arrests come with the city on edge after Swiss authorities on Thursday opened a probe relating to a "terrorist threat in the Geneva region", prompting the region to raise its alert level to three on a five-point scale.

Armed police were deployed at sensitive locations across Geneva, which borders France and is home to the United Nations' European headquarters.

The Le Temps daily on Friday cited an unnamed source close to the case as saying the Swiss had received a tip-off from US intelligence about a jihadist cell in Geneva.

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Pictures of four individuals suspected of links to the Islamic State group, which claimed last month's Paris attacks, were published by media across the country.

Authorities in Geneva had said that the search for possible extremists was being conducted "in the context of the investigation following the Paris attacks".

But multiple sources, who requested anonymity, said there did not appear to be a direct link with the coordinated November 13 gun and suicide bombing attacks that left 130 dead in the French capital.