Switzerland's Attorney General's Office and the Swiss Federal Police Office say they have opened criminal proceedings against two Syrian citizens on suspicion they manufactured, concealed and transported explosives and toxic gases and also allegedly violated bans on militants groups like al-Qaeda and ISIS.

The attorney general said in a statement the two people, who were not further identified, were arrested Friday in the Geneva area.

At a news conference Saturday, the Geneva prosecutor said the two Syrians were arrested in a vehicle containing traces of explosives, and that they have not been clearly linked to four men with suspected ties to the Islamic State group who are wanted by Swiss authorities.

Prosecutor Olivier Jornot provided few new details Saturday.

Geneva has been under heightened security measures since Thursday, with authorities hunting the four suspects with alleged ISIS links who are believed to be plotting a "specific" attack in the city. Authorities have not identified the suspects.

Geneva high alert

Armed UN security officers guard the European headquarters of the United Nations in Geneva, which has been on high alert since Thursday as authorities search for four people believed to have ties to ISIS. (Salvatore Di Nolfi/EPA)

Police in the Swiss city, home to the European headquarters of the United Nations, the Red Cross and many banks and trading houses, moved into a high state of alert after a suspicious Belgian-registered vehicle fled from a late-night police check and crossed the border into France.

Geneva's Le Temps newspaper reported on Thursday that one of the two occupants was a friend of Salah Abdeslam, the man wanted in connection with the Nov. 13 Paris attacks.

The Geneva department of security said in a statement Friday that "the level of vigilance remains unchanged for now" and that the reinforced police deployments will be maintained

The greater vigilance has meant the public, private security teams and others have been on a greater lookout for suspicious activities: At Geneva's airport, bomb squads cordoned off and suspended access to some areas to deal with two pieces of abandoned luggage.

Airport spokesman Bertrand Staempfli says no bomb was found and flights were not delayed or disrupted. Authorities located the owner of one bag found abandoned near a security checkpoint, and another bag was destroyed by bomb squads.

Across town, the head of Geneva security met with the top official at the UN office in Geneva, one of the city's many diplomatic sites where guards carrying submachine guns have been deployed.

With files from Reuters