A spokesman for the C.I.A. declined to comment.

The court, which rules on questions of law, returned the cases against five Italian secret service agents, including the former head of Italy’s military intelligence agency, to trial. The Italian officers were acquitted in two lower courts, which had ruled the evidence against them to be state secrets and thus inadmissible. They will now be tried in a Milanese appellate court.

The case made headlines as the first in the world to scrutinize — and legally condemn — the American practice of rendition, in which suspected Islamic militants were abducted in one country and transferred to another, often one where torture was permitted. The program, begun amid the heightened fears after Sept. 11, has since been ended.

Hassan Mustafa Osama Nasr, also known as Abu Omar, was abducted on Feb. 17, 2003, as he was walking to his mosque. Prosecutors said he had been taken to an American air base in Italy and flown to Germany and then on to Egypt, where Mr. Nasr says he was tortured. He has since been released.

The Americans were convicted in 2009, and an appellate court upheld the verdicts in 2010.

A lawyer for two of the American defendants, Alessia Sorgato, said she was surprised by Wednesday’s ruling. She had argued that her clients had not been properly notified of the charges against them, because prosecutors had sought to serve them papers in Italy and not in the United States. “This verdict is really disappointing,” Ms. Sorgato said. “This is it; I can’t do anything else.”

Cesare Bulgheroni, the lawyer representing the Air Force colonel, Joseph L. Romano, said his client would challenge the ruling before the European Court of Human Rights. “We plan to go forward,” he said.