"He is suspected of having committed war crimes as a member of the Kosovo Liberation Army," said Folco Galli, a ministry spokesman.
"He is wanted by Serbian authorities, and is currently under detention in view of extradition," said the spokesman, who would not name the detainee.
The man, identified by Serbian local news agency Presheva Jone as Shemsi Nuhiu, has opposed the extradition.
Swiss authorities are currently examining the extradition request, Galli said, adding that the former KLA member can still appeal if Switzerland decides to accept Serbia's request.
Belgrade has accused the man of committing war crimes against Serbian civilians in 1999, at Gnjilane, close to Kosovo's capital Pristina.
He is believed to be from a group of ethnic Albanian guerrillas who allegedly abducted around 150 people and killed at least 50 at the end of the 1998-1999 Kosovo conflict.
According to the Serbian extradition request, the man holds Serbian nationality.
Galli said he currently lives in Vevey, Switzerland, but does not hold Swiss nationality.