LONDON -- The international fallout from the apparent CIA abduction of an Islamic militant cleric off the streets of Milan highlights the potential for such tactics to heighten friction between the United States and its European allies. The issue is how to wage the fight against terrorism.
Prime Minister Silvio Berlusconi summoned the US ambassador, Mel Sembler, on Friday. He demanded that the United States show ''full respect" for Italy's sovereignty.
Berlusconi, a key ally of President Bush on the Iraq war despite its unpopularity in Italy and in much of Europe, called on the United States to explain the kidnapping of the Egyptian cleric in Milan, just one month before the United States launched its invasion of Iraq in March 2003.
European intelligence officials, Western diplomats, and specialists on terrorism say the brazen operation -- whether it had approval from a level of Italian intelligence or not -- has focused a harsh European spotlight on a dark corner of the US antiterrorism campaign.
The CIA's increasing use of ''extraordinary renditions," in which US authorities abduct terrorism suspects and transfer them to third countries that are known to use torture, has inflamed passions across Europe among human rights activists and the intelligence community.
It has raised concern that such tactics not only flout international law, but that they may also ultimately undercut much-needed cooperation between the United States and its European allies.
Tom Parker, a senior official in the British government's counter-terrorism operations in the 1990s who has subsequently worked in counterterrorism and international law for the United Nations, said: ''There is no doubt that this incident in Milan and others like it in other cities in Europe will undercut cooperation between governments and the US."
A European counterterrorism official in Brussels, who spoke on condition of anonymity, said there were ''many unknowns" about what had happened in Milan, and about whether the CIA had Italian approval for the operation.
But the official added, ''There is a public perception issue, and that will almost inevitably hurt cooperation between the US and Europe on fighting terror."
That is ''unfortunate," the official added, because there has been ''very strong cooperation recently."
The Italian government has publicly insisted that such approval was neither sought nor granted. And an Italian magistrate has issued arrest warrants for the 13 alleged CIA agents who are reported to have carried out the ''snatch-and-grab" seizure of Osama Mustafa Hassan Nasr, 42, who was then flown by the CIA agents to Egypt for interrogation.
The imam told his family he had been tortured with electric shocks during his detention.
Hassan, also known as Abu Omar, was being investigated in Italy as part of a terrorism inquiry at the time of his abduction.
A report published recently by the New York University Law School's Center for Human Rights and Global Justice found that the use of ''extraordinary renditions" has increased dramatically in recent years. Former CIA officials have said that as many as 150 ''extraordinary renditions" have been carried out since the attacks of Sept. 11, 2001.
Jerrold Post, a former high ranking CIA counterterrorism official with more than 25 years of service, said in a telephone interview that ''if this operation was carried out without permission, that would be a major departure from the way things were done in the past. . . . The importance of close sharing with colleagues in the battle against terrorism has always been associated with not acting in a unilateral fashion."
Post said that the Italian intelligence agencies have been known as sophisticated and experienced since the struggle against leftist militants, particularly the Red Brigades, and that there was a tradition of strong cooperation with the United States.
''I would be quite surprised to learn that such action was taken given how much it could undermine cooperation," added Post, who now teaches at George Washington University and has written extensively on the psychology of terrorism.
Parker, the former British counterterrorism official now researching counter-terrorism policies at Brown University, said, ''the political reality is that now that these operations are being exposed, they are having a blow-back effect on the goals of the US counterterrorism strategy. . . ."
''There is a tipping point at which these kinds of extreme measures become counterproductive. If you are going to pursue these, you have to presume that it is going to be exposed and so you have to pick and choose carefully."
Frank Anderson, former head of the CIA's Near East Division, also questioned whether the Nasr abduction was worth the risk. ''It would appear that this guy was just not a high-value enough target," Anderson said.
Europe has been the scene of some of the most visible renditions in recent years.
In Sweden, a parliamentary investigation was launched into the alleged abduction of two Egyptians in December 2001. According to newspaper and Swedish television reports, Swedish ministers voted secretly to expel two terrorism suspects, Muhammed Zery and Ahmed Agiza, took the men into custody, and then asked the CIA to fly them to Cairo.
The disclosures of the Swedish involvement with the CIA-led operation prompted the director of Sweden's security police, Klas Bergenstrand, to promise last week that his agency would never let foreign agents take charge of such a case again.
''In the future we will use Swedish laws, Swedish measures of force and Swedish military aviation when deporting terrorists," Bergenstrand told a number of international reporters. ''That way we get full control over the whole situation."
The German parliament also has launched an investigation into a rendition. On Dec. 31, 2003, says Khaled el-Masri, a German citizen, he was pulled from a bus at the border of Macedonia, interrogated, and finally flown to a US-controlled jail in Afghanistan. In an extensive interview with the British newspaper the Guardian, el-Masri alleged that after five months in the jail, he was dumped in Albania before making his way back to Germany.
In another highly visible European case reported by the magazine The New Yorker, six men were arrested by Bosnian authorities in October 2001, after US officials had reported that they were planning to bomb US and British embassies.
In January 2002, the Bosnian Supreme Court ordered the men released for lack of evidence.
Instead, the men were removed from prison; they are now alleged to be at the US military holding facility in Guantanamo Bay.
Globe correspondent Sarah Liebowitz in London contributed to this report.