ROME - A trial in which 25 CIA agents are accused of kidnapping a terrorism suspect ran into serious difficulties last night when Italy's constitutional court upheld key objections raised by the Italian government.

Prosecutors say the suspect - Hassan Mustafa Osama Nasr, also known as Abu Omar - was snatched off the streets of Milan six years ago and flown to Egypt. There, he has claimed, he was tortured under interrogation.

The constitutional court decided that in building up their case against the US intelligence operatives and another eight defendants the prosecutors violated state secrecy. In particular, the judges upheld objections to the use of material gathered in a raid in 2006 on an unofficial outpost of the intelligence service in Rome.

The court revoked several passages in the indictment. But it was not immediately clear if their ruling would mean the trial had to be called off.

The case represents the most comprehensive effort anywhere to apply the law to an alleged extraordinary rendition, in which a terrorist suspect is seized by US officials in a foreign country. In several renditions since the Bush administration launched its "war on terror" the suspects are alleged to have been transferred to third nations where torture was used.

Italy's prime minister, Silvio Berlusconi, headed a previous government at the time of Omar's disappearance. He and the head of Italy's last, centre-left administration, Romano Prodi, both endorsed challenges to the trial's legality.

The court did not uphold all the state's arguments. In its one-page ruling, it said the prosecutors were entitled to order wiretaps to be put on the telephones of Italian intelligence officers.