A Swiss national, working for the medical humanitarian aid agency Médicins Sans Frontières MSF (Doctors Without Borders), is believed to have been kidnapped with four other colleagues in Syria on Thursday.
MSF confirmed on Saturday that the Swiss, Swedish, Peruvian, Danish and Belgian nationals had gone missing. The Swiss foreign ministry said it was aware of the incident, but no further details were given.
The international media has reported that the five were abducted from an MSF office in northern Syria by an unidentified group.
MSF currently has teams stationed with international and local staff in six hospitals and four health centres in the region. The international organisation provides medical services in regions hit by conflict, natural disasters and other emergencies.
Syria has been ravaged by civil war since March 2011, with estimates putting the loss of life at well over 100,000. Some 11.5 million people in Syria and the surrounding area are dependent on humanitarian aid.