Spokespeople from the various chapters of the group in four European countries confirmed the information regarding the MSF employees taken Thursday night from a house they were using in war-ravaged Syria.
The Peruvian foreign ministry meanwhile said it was working to confirm media reports there that the fifth MSF staff member taken was from the South American country.
"I can't give you any details for security reasons, but one of them is of Swiss nationality," MSF Switzerland spokeswoman Sibylle Berger told AFP.
"We haven't had contact with them since then," she said.
MSF has declined to provide further information about the staff members, not even providing their ages or saying whether they are men or women.
Belgian Foreign Minister Didier Reynders however told broadcaster RTL-TV that the Belgian national was a nurse in his 30s.
He emphasised though that it had not yet been established that the five had been kidnapped.
It remained unclear who had taken the MSF staff and the organisation has so far refused to provide the exact location of the house they were taken from.
"We are still trying to analyse the situation and see what we can do to help our colleagues," Berger said, explaining why the organisation was being so tight-lipped.
In a statement Friday, the organisation said only that the five had been taken "apparently for questioning".
"MSF is in contact with all the appropriate actors as well as the families of the colleagues and is doing everything possible to reestablish contact with these colleagues," spokeswoman Samantha Maurin said in that statement.
