Amid an outcry over reports that the Americans were absolving US soldiers of any blame in the friendly-fire shooting, Berlusconi apologised for what he called "an unfortunate leak", suggesting that the investigation was completed.
He spoke shortly after the US ambassador to Italy met the prime minister's top aide on Tuesday to see whether crucial differences over the investigation could be worked out.
The government "will speak at the opportune moment", briefing parliament when the US-Italian investigation is done, Berlusconi said.
He offered those assurances at the start of a speech to the Chamber of Deputies to present his new government, which faces a confidence vote in the legislature on Wednesday.
In Washington, US Defence Secretary Donald Rumsfeld and General Richard Myers, chairman of the US Joint Chiefs of Staff, acknowledged on Tuesday that the Italian officials who participated in the investigation had not signed off on the report's conclusions.
"My latest information
is that they have not come to a final agreement on a
US defence secretary
They provided no details about the report.
"My latest information is that they have not come to a final agreement on a joint report," Rumsfeld said of US and Italian investigators.
"It's an investigation, it was done together, intimately, and I think that we'll just have to wait and see what they come out with."
Myers said the final report would be issued in Baghdad.
On Monday, a senior US defence official in Washington said US soldiers guarding the checkpoint near Baghdad's airport generally followed instructions for handling potential threats when they fired at a car in which agent Nicola Calipari was riding on 4 March.
Calipari, hailed at home as a hero, had just helped to free an Italian hostage in Baghdad and was accompanying her to the airport when he died in a hail of US gunfire at a temporary checkpoint.
Nicola Calipari has been hailed
as a hero in Italy
The hostage and another agent in their car survived, and their testimony on the shooting sharply conflicted with official US accounts.
Earlier in the day, the Italian opposition attacked the US for allegedly concluding that American soldiers bore no responsibility for the shooting that caused Calipari's death.
One opposition leader, Giuseppe Fioroni, denounced any absolution of blame as an "unacceptable act of arrogance toward Italy".
Fifty Italian opposition senators wrote to US senators to urge American authorities to cooperate with Italian investigators and not "spoil" the friendship between the two allies.
A finding that US soldiers bore no responsibility could rock Berlusconi politically. There was widespread public anger over his support for the Iraq war.
The prime minister is a staunch US ally and sent about 3000 troops to Iraq.
The talks between US ambassador Mel Sembler and cabinet undersecretary Gianni Letta lasted roughly an hour at the prime minister's office. Neither side immediately made any comment.
Giuliana Sgrena said her vehicle
was not travelling at high speed
Going into the meeting, the ambassador said he intended to "listen and to try to determine a way forward", a US official said.
The two Italian members on the joint investigation - a general and a diplomat - reportedly have refused to sign the as-yet- unpublished report because of the clash of views.
Italian state TV reported on Tuesday that the Americans concluded that the car Calipari, the former hostage and a second intelligence agent were riding in at the checkpoint was travelling too fast - at 80kph - raising the risk that the vehicle could be a security danger.
Point of difference
But the former hostage, journalist Giuliana Sgrena, and a second intelligence official who was driving, testified that the Toyota Corolla was travelling at about half that speed.
Another crucial point of difference is whether warning signals were given in time for the car to stop.
Writing on the front page of the daily Il Manifesto, which sent her to Iraq, Sgrena denounced the US conclusions of no-blame as a "slap" for Berlusconi.
Rome prosecutors, who are conducting their own investigation, have been waiting for the end of the US-Italian inquiry to inspect the car, which was expected to be flown to Italy later on Tuesday aboard an Italian Air Force plane.
"It's enough to see the car," Sgrena wrote in Il Manifesto. "The front windshield is intact, while the side windows and the one behind are shattered."
Calipari died as he used his body to shield Sgrena from gunfire.