But the country's prime minister, Silvio Berlusconi, rejected a call to discuss the issue in parliament.
In a brief statement to the chamber of deputies on Tuesday, Berlusconi said news reports about the purported findings of the joint investigation were leaks and insisted the study was not over.
"The government ... will only speak about this when all the results of the inquiry are finalised," Berlusconi said, adding his government was in contact with the US administration.
Military intelligence officer Nicola Calipari died when troops at a US checkpoint opened fire late on 4 March as he was driving to Baghdad airport with Italian journalist Giuliana Sgrena after obtaining her release from kidnappers.
A US army official, briefing reporters in Washington on the preliminary results of the report, said on Monday the soldiers had only followed their rules of engagement and should, therefore, face no charges of dereliction of duty.
The official said Italy, a close US ally in Iraq, had balked at endorsing the report. Rome disagreed with its findings on the car's speed and whether the Italians kept US troops informed.
The report comes at a time when
Berlusconi is under pressure
"A unilateral conclusion absolving anyone of blame that the Italian side does not accept is an insult to the truth and to the memory of Nicola Calipari and a serious act of arrogance towards Italy," one opposition lawmaker, Giuseppe Fioroni of the centre-left Margherita Party, said in a statement.
The report was the latest in a series of US military investigations into the killing of civilians by American forces in Iraq to have found no wrongdoing.
Slap in the face
The New York-based Committee to Protect Journalists (CPJ) called for a throrough and credible investigation and said Italian-US disagreement on the probe was troubling.
"The failure to reach an agreement would be a missed opportunity to address the serious issue of safety for civilians - including members of the press - at US checkpoints," CPJ Executive Director Ann Cooper said in a statement.
The case comes at an awkward time for Berlusconi, who faces confidence votes in the chamber of deputies on Wednesday and the senate on Thursday on a new cabinet after a coalition mutiny over a heavy regional election defeat in early April.
Reporter Sgrena described the
findings as a slap in the face
Sgrena, a veteran war correspondent for the newspaper Il Manifesto, who was wounded in the shooting, called the findings a slap in the face, and again alleged that Calipari had been killed deliberately.
"Nicola Calipari was murdered. Don't use the word accident. Now we want the truth, and we want to know who gave the order to open fire on that car," she said.
A staunch ally of the US in Iraq, Berlusconi's decision to send troops there was deeply unpopular and, with a general election now due in 2006, he has already said they will start returning home from September.
Italian newspapers said the leaking of the report appeared designed to limit Italy's options, with Berlusconi now facing a tough choice of whether to disagree openly with Washington or try to sweep the findings under the carpet.
Calipari, feted in Italy as a national hero, was fatally wounded when he shielded Sgrena from gunfire as their car approached a checkpoint near the Baghdad airport, where a plane was waiting to fly them back to Italy.
The car involved was due to arrive in Italy on Tuesday from Baghdad for forensic tests as part of a separate judicial investigation by Rome magistrates.
The chairman of the Italian senate defence commission, Domenico Contestabile, who is a member of Berlusconi's Forza Italia Party, said it would be very difficult for the magistrates to establish what happened in Iraq from Italy.