The CIA's Milan station chief at the time, Robert Seldon Lady, was sentenced to eight years in prison and the other Americans to five years, all in their absence in the landmark trial.

The two Italians were given three-year prison terms following the first trial involving the transfer of a “war on terror” suspect by CIA operatives thought to have sent scores of people to countries known to practise torture.

The CIA chief for Italy at the time, Jeffrey Castelli, and the then head of Italian military intelligence SISMI, Nicolo Pollari, were protected by state secrecy rules, while two other American defendants benefited from diplomatic immunity, Judge Oscar Magi said.

U.S. President Barack Obama's administration expressed disappointment at the verdict.

“We are disappointed by the verdicts against the Americans and Italians charged in Milan for their alleged involvement in the case involving Egyptian cleric Abu Omar,” State Department spokesman Ian Kelly said in Washington.

Prosecutor Armando Spataro hailed the verdict, saying the trial, which opened in June 2007, had demonstrated “the truth of the investigation.”

“We don't need torture or rendition or secret prisons,” Spataro told AFP. “We need full respect of the law otherwise we give the terrorists more motivation.”

Spataro had sought a 13-year jail term for Castelli and Pollari — who was forced to quit over the affair.

Osama Mustafa Hassan, an imam better known as Abu Omar, was snatched from a Milan street on February 17, 2003, in the operation coordinated by the CIA and SISMI.

The radical Islamist opposition figure, who enjoyed political asylum in Italy, was allegedly taken to the U.S. air force base in Aviano, northeastern Italy, then flown to the U.S. base in Ramstein, Germany, and on to Cairo where he says he was tortured.

The “extraordinary rendition” programme was set up by the administration of then president George W. Bush in the wake of the September 11, 2001, terror attacks.

The imam's captors failed to take many standard precautions, notably speaking openly on cell phones, leaving investigators to suspect that the Americans had cleared their intentions with senior Italian intelligence officials.

The rights group Human Rights Watch hailed the verdict, even though the two highest-ranking officials were not convicted.

“No one was found innocent,” noted Joanne Mariner, while lamenting those who “got off the hook because of the Constitutional Court's overbroad interpretation of state secrecy.”

“The Italian government was found responsible for collaborating with the CIA. It was a brave ruling for an Italian court,” Mariner told AFP.