Italy's center-left opposition on Thursday urged the government to seek an apology from the United States for the "friendly fire" that killed Italian agent Nicola Calipari in Iraq.

Prime Minister Silvio Berlusconi's administration was also asked to begin preparing the withdrawal of 3,000 Italian troops from Iraq although most of the opposition said this request was unconnected to the Calipari affair.

"It's time the United States government apologized to Italy," said Democratic Left leader Piero Fassino in a speech to the Houseshortly after Berlusconi told lawmakers that the United States wasresponsible for Calipari's death even though the tragedy was unintentional.

"There have been condolences and appreciation for Calipari, rightly defined a hero, but no apology," he continued. "Even if itwas an unintentional incident, someone is to blame and it's right that they apologize."

Fassino, who heads Italy's biggest opposition party, urged the government to seek the truth about the incident but agreed with Berlusconi that relations with the US should not be affected by it.

Echoing a statement by opposition leader Romano Prodi on Wednesday, Fassino called on the government to make preparations for the withdrawal of Italian soldiers from Iraq in the light of the "new phase" under way in the country.

Prodi said that, while there was "no direct link" between the Calipari affair and the pull-out of troops, the episode should prompt both the opposition and the government to "accelerate a reflection on the mode of withdrawal."

Nicolas Calipari was killed on March 4 by American soldiers as he was accompanying a newly freed Italian hostage outside the Baghdad airport.

Addressing the parliament on Thursday, Berlusconi said he disagreed with some of the US military's conclusions into the shooting death of the Italian agent, saying the responsibility of the US troops cannot be ruled out.

He, however, said the differences won't affect Italy's friendship with Washington or its deployment of troops in Iraq.