Italian magistrates in Milan have issued arrest warrants against six more CIA agents accused of kidnapping a terrorism suspect.

Some 13 warrants were issued last month against people linked to the CIA in connection with the alleged abduction.

Radical cleric Hassan Mustafa Osama Nasr, who runs a mosque in Milan, is said to have been seized and taken to Egypt where he claims he was physically abused during interrogation.

The abduction took place in February 2003 when both US and Italian authorities were investigating his alleged links to terrorism, including recruiting fighters for Iraq.

The judge in charge of the case described it as a grave violation of Italian sovereignty and Prime Minister Silvio Berlusconi's government called in the US ambassador to discuss the situation.

Relations between Rome and Washington have been strained since US troops in Iraq shot dead an Italian agent as he escorted a released hostage to safety.

PHOTO CAPTION

The CIA symbol is shown on the floor of its headquarters in Langley, Virginia. (AFP)