ROME, Italy (CNN) -- An Italian judge ruled Wednesday that Italian Prime Minister Silvio Berlusconi may be called as a witness at the trial of 26 Americans, mostly CIA agents, in connection with the alleged kidnapping of a Muslim cleric, a Milan court official said.
Italian premier Silvio Berlusconi has been called to testify because he was prime minister five years ago.
Judge Oscar Magi ruled Berlusconi's testimony is admissible at the trial, essentially giving defense attorneys the right to call the premier to the witness stand, said the court official, who was not authorized to speak with the media.
Berlusconi is not accused of any wrongdoing, but because he is a witness, he must appear in court. In Italy, only defendants may opt not to appear.
Berlusconi will testify as someone informed about the facts in question because he was prime minister at the time of the alleged abduction more than five years ago. Magi also ruled that former prime minister Romano Prodi may also be called to the witness stand.
The proceedings center on the alleged kidnapping of Osama Nasr Mostafa Hassan, an Egyptian-born Muslim cleric also known as Abu Omar, in February 2003.
At the time of his disappearance, Milan prosecutors were investigating him for alleged links to terrorism.
Prosecutors allege that a CIA team working with Italian intelligence officials seized him from a Milan street, eventually flew him to Egypt, and used torture as part of an interrogation there.
Italian authorities last year indicted 26 Americans and five Italians for kidnapping in the case.
The Italians include the former head of Italian intelligence, Nicolo Pollari, and one of his deputies. They testified in preliminary hearings that Italian intelligence played no role in the alleged abduction.
None of the Americans is in custody in Italy and the Italian government has not asked for their extradition; they are being tried in absentia.
Italy's constitutional court is being asked to rule whether documents Pollari wants to use to clarify his position and defend himself are admissible in court and whether prosecutors investigating the case violated state secrecy rules.
Italian media report a ruling on that could come July 8. Should the court rule that prosecutors breached national security, the whole trial would be invalidated.
The trial deals with a practice that human rights groups call "extraordinary rendition," and they say the United States has often sent suspects to countries that practice torture.
Washington acknowledges making secret "rendition" transfers of terrorism suspects between countries but denies using torture or handing suspects over to countries that do.
In an earlier interview, former CIA analyst Michael Scheuer said the Italian military secret service had approved the operation involving Hassan, and CIA sources who refused to be named told CNN in 2005 that the agency had briefed and sought approval from its Italian counterpart for such an abduction.
The then Italian government of Berlusconi has vigorously denied having authorized Hassan's kidnapping, which it called illegal.
CNN's Alessio Vinci contributed to this report.