Prosecutors said Wednesday they had arrested two Italian intelligence officers as part of their investigation into the alleged CIA kidnapping of an Egyptian cleric in Milan, providing the first official sign that Italian agents were involved.

They also announced they were seeking the arrest of four more Americans after earlier demanding the extradition of 22 purported CIA agents.

The arrests of the two SISMI intelligence officials fueled allegations by a European investigator that Italy and 13 other European countries had aided the United States with the secret transfer of terror suspects to detention centers around the world.

Osama Moustafa Hassan Nasr, an Egyptian cleric and terrorist suspect also known as Abu Omar, was allegedly kidnapped from a Milan street on Feb. 17, 2003. Prosecutors say the operation represented a severe breach of Italian sovereignty that compromised their anti-terrorism efforts, and have already incriminated 22 purported CIA agents.

Prosecutors say Nasr was taken by the CIA to the joint U.S.-Italian Aviano air base, flown to Germany and then to Egypt, where he says he was tortured.

The operation is believed part of an alleged CIA program in which terrorism suspects are transferred to third countries where some allegedly are subjected to torture. The CIA describes such operations as "extraordinary renditions."

Prosecutors and a lawyer for Nasr say he is being held in a Cairo prison.

Italy's new, center-left government released a statement late Wednesday saying that its intelligence services had denied any part in the alleged kidnapping. It vowed to cooperate with the investigation.

Prosecutors in Milan said three of the latest Americans being sought were CIA agents, while the fourth worked at Aviano. Their statement did not provide names of those targeted.

It said the two Italians, at the time of the kidnapping, were the director of SISMI's first division — dealing with international terrorism — and the head of the agency's operations in northern Italy.

Italian reports identified the two as Marco Mancini, now the head of military counterespionage, and Gustavo Pignero, and said they were charged with kidnapping with the aggravating circumstance of abuse of power.

Communist politician Marco Rizzo called the case "shocking," and blamed the conservative government of former Premier Silvio Berlusconi — a firm U.S. ally — for allowing foreign secret agents free rein on Italian soil.

"The ceding of sovereignty at the expense of our country is disturbing," Rizzo was quoted as saying by the Apcom news agency, "as is the manifest violation of international law."

"The arrest ... confirms the collusion of EU member states in CIA abuses on European territory," said a statement by two Green members of the European Parliament, Cem Ozdemir and Raul Romeva. "Today's arrest leaves this complicity beyond doubt."

They added, "This arrest is only the tip of the iceberg."

Some politicians in Italy, however, criticized prosecutors for hurting the fight against terrorism.

"Osama bin Laden is happy. In my country today, instead of arresting terrorists we're arresting those who are hunting terrorists," said Jas Gawronski, an Italian member of the European Parliament and member of a committee investigating questionable CIA activities. He also is a former Berlusconi spokesman.

European investigator Dick Marty, a Swiss senator, reported to Europe's top human rights body in June that 14 European countries, including Italy, had aided the movement of detainees who said they had been abducted by U.S. agents and secretly transferred to detention centers around the world.

The alleged involvement of Italian officials came after news reports here insisted for several months that Italy played some role in the operation. A report published in La Repubblica in May claimed that the SISMI's operations unit had cooperated with the Americans.

Berlusconi always denied the suggestions, and maintained his government and Italian secret services were not informed about the operation and had not taken part in it. In March, SISMI director Nicolo Pollari told EU lawmakers that Italian agents played no part and had no knowledge of the operation.

Milan Prosecutor Armando Spataro, who is leading the investigation, has been seeking the extradition of the 22 purported CIA agents accused in the abduction. The Berlusconi government decided against forwarding Spataro's extradition request to Washington, but Spataro has said he would ask the new government led by Romano Prodi to make the request.