A leaked interim report by Swiss federal prosecutors has allegedly indicated that the CIA used Swiss airspace to fly a Muslim cleric to Egypt for interrogation.
Justice Minister Christoph Blocher informed his cabinet colleagues on Friday about the prosecutors' findings, part of an investigation launched late last year.
The Swiss tabloid Blick reported on Saturday that the report declared it was "probable to the point of certainty" that Egyptian cleric and terrorist suspect Osama Moustafa Hassan Nasr, also known as Abu Omar, was transported through Swiss air space.
The spokesman for the justice ministry, Livio Zanolari, confirmed that Blocher had received the report and delivered a verbal statement on the investigation. He would not comment on the content of the report.
The prosecutor's office also refused to comment.
The Swiss foreign ministry said in February that the American government had assured it had not used Swiss air space or airports for prisoner transfers.
Based on these assurances, Switzerland renewed permission for the US to use its airspace, a move that had been delayed while it waited for Washington's explanations.
Federal prosecutors opened their investigation into the so-called rendition flight last year after air traffic data revealed that an aircraft travelled from Germany to northern Italy and back again on February 17, 2003.
This was the day Italian prosecutors claim Abu Omar was abducted from a Milan street. Zanolari confirmed that the Swiss prosecutors were looking only into this one case.
In June, the Federal Office of Civil Aviation said CIA planes landed in Switzerland 58 times, and flew through the country's air space 73 times, between February 2001 and February 2006.
According to Zanolari, there was no evidence at present to suggest a plane carrying prisoners had landed in Switzerland.
Dick Marty, a Swiss senator and chairman of the Council of Europe's Committee on Legal Affairs and Human Rights, carried out an investigation into alleged CIA activities at the behest of the human rights watchdog.
His final report, released in June, claimed that 14 European countries had colluded with the American intelligence agency to set up secret flights and detention centres in violation of international human rights laws.
Marty provided no direct evidence but said that most European governments did not seem eager to help him establish the facts about renditions.
He relied mostly on flight logs provided by the Eurocontrol air traffic agency, witness statements, as well as judicial and parliamentary inquiries in various countries.
Marty also accused the Swiss government of having "deliberately ignored allegations" of suspect aircraft transiting through the country's airspace, which were eventually confirmed by the aviation office.
Under the CIA policy of rendition, prisoners are moved to third countries for interrogation. But Washington denies they are subjected to torture.
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Extraordinary rendition is an American extra-judicial procedure. It involves sending untried suspects or alleged supporters of groups that the US considers to be terrorist organizations, to countries other than the United States for imprisonment and interrogation.
Critics say these renditions are used to avoid US laws prescribing due process and prohibiting torture.
The procedure was allegedly developed by the CIA in the mid-1990s as it attempted to track down and dismantle militant Islamic organizations in the Middle East, particularly al Qaeda.