Rome ? In a case testing Italian-U.S. relations, a Milan prosecutor sought arrest warrants Wednesday for six more purported CIA operatives, accusing them of helping plan the kidnapping of an Egyptian radical Muslim cleric.

An Italian court has already issued warrants for 13 purported CIA officials accused of helping carry out Osama Moustafa Hassan Nasr’s 2003 abduction.

But the court initially turned down a request to issue arrest warrants for the six who prosecutor Armando Spataro says helped plan the abduction.

Cell phone tracking shows the six made nearly 100 inspections of the Milan area where the cleric was seized, and that they studied his habits as well as the best routes to the highway used to bring the Egyptian to Aviano, a joint U.S.-Italian air base north of Venice, according to the prosecutor’s request, obtained by The Associated Press.

“There were no doubts” the six were part “of a single group of Americans who came to Milan to carry out the operation,” the prosecutor said in his appeal.

Nasr, known as Abu Omar, was allegedly snatched on a Milan street Feb. 17, 2003, flown from Aviano to an air base in Germany and then to Egypt, where he reportedly was tortured.

The operation purportedly was part of the CIA’s “extraordinary rendition” program, in which terror suspects are transferred to third countries without court approval, subjecting them to possible ill treatment.

The court-appointed attorney for the six, Guido Meroni, said there was no proof of his clients’ direct participation in the alleged kidnapping.

The CIA has declined to comment on the case, which has strained relations between the two allied nations. Premier Silvio Berlusconi has a close relationship with President Bush, but ties between Rome and Washington were previously jolted by the shooting death of an Italian agent by U.S. troops in the Iraqi capital, Baghdad, in March.

Italy’s magistrates are fiercely independent of the government.

After initial outrage in Italy, Berlusconi told the U.S. ambassador he expects Washington to “fully respect Italian sovereignty.”

Germano Dottori, a political analyst at the Center for Strategic Studies in Rome, said the Milan case could damage cooperation between the two countries’ secret services.

“Among U.S. intelligence officers you might see a reduced trust in their Italian counterparts,” he said.