But the seven-member Cabinet said last year that it could not tolerate the use of Swiss airspace for an abduction, citing evidence that basic norms of international law were violated.
The investigation concerned the alleged kidnapping of Osama Hassan Mustafa Nasr, known as Abu Omar, from a street in Milan. The CIA allegedly flew Nasr from Aviano air base in Italy across Switzerland to Ramstein air base, Germany, and then on to Cairo, Egypt, on Feb. 17, 2003.
Nasr, who was allegedly tortured during his imprisonment in Egypt, was ordered released last year by an Egyptian State Security Court that ruled his detention for four years in Egypt was unfounded.
Balmer said Swiss prosecutors "will not provide any further information on this case until the circumstances allow" it. She declined to comment further.
Italy has charged 26 Americans in the alleged operation — all but one identified by Italian prosecutors as CIA agents — but a Milan judge suspended the trial in October pending a decision by the country's highest court on a government challenge that could scuttle the case.
The Italian court ruling should show whether the kidnapping trial will be permitted to publicly air details of the U.S. so-called extraordinary rendition program — moving terrorism suspects from country to country without public legal proceedings.
Critics of the program say some suspects have been tortured after being delivered to certain countries.
Under Swiss law, a sentence of up to three years in prison can be imposed on anyone who undertakes actions for a foreign government on Swiss territory without permission.
The law also specifies a prison term of at least one year for abduction through violence, trickery or threats, followed by delivery to a foreign agency or organization outside Switzerland.
All the accused Americans have left Italy.