Italy's highest court has upheld the guilty verdicts against 23 agents of the US Central Intelligence Agency (CIA) for the 2003 abduction of an Egyptian imam in Milan.
The court made the ruling on Wednesday, which also ordered a re-trial for five Italian ex-spies accused of taking part.
The cleric, known as Abu Omar, was allegedly flown to Egypt and tortured.
The agents, one of whom an air force pilot, were all being tried in absentia in one of the world's biggest court cases against the US "extraordinary rendition" programme to interrogate alleged Islamist "militants" after the September 11, 2001 attacks.
They were originally sentenced in November 2009 to five to eight years in prison and in December 2010 had their sentences increased to seven to nine years on appeal and ordered to pay damages to the imam.
Italy's justice ministry is now obliged to make a formal request for the extradition of the agents, legal sources said, but the United States has already refused.
The agents, who remain at liberty but risk arrest if they travel to Europe, are believed to be living in the United States and are unlikely to serve their sentences.
As part of the ruling, the court ordered the seizure of the Italian home of one of the agents, Bob Seldon Lady, former head of the CIA station in Milan.
A radical Islamist opposition figure, Abu Omar, better known as Osama Mustafa Hassan, was snatched from a street in Milan in 2003 in an operation co-ordinated by the CIA and the Italian military intelligence agency SISMI.
Abu Omar, who enjoyed political asylum in Italy at the time, was then allegedly taken to the Aviano US air base in northeastern Italy, flown to a US base in Germany, and on to Cairo, where he says he was tortured.
In Wednesday's ruling, the court also said that two former heads of SISMI, Nicolo Pollari and Marco Mancini, should be re-tried.
The two had been acquitted by the appeals court in 2010 in a ruling that said producing evidence against them would have violated state secrecy laws.
Three lower-level Italian agents will also be re-tried, the court said.
To conclude, the court upheld a two year and eight month prison sentence against former military intelligence officials Pio Pompa and Luciano Seno.
The "extraordinary rendition" programme was launched in 2003 by then US president George W. Bush and saw scores of suspects returned to their home countries, some of which were known to use torture.