Nicola Calipari, a senior Italian intelligence agent, was shot dead on March 4 when US soldiers fired at his car as he took the reporter, Guiliana Sgrena, to Baghdad airport.

A report leaked by an American army official in Washington last night was said to have cleared US troops of any culpability for his death. The official said the soldiers had followed their rules of engagement and should not therefore face charges of dereliction of duty.

The probe was conducted in co-operation with the Italians, but the official conceded that Italy, a close US ally in Iraq, disagreed with its findings.

In a front page editorial in her left-wing daily Il Manifesto, Sgrena called on Silvio Berlusconi, the Prime Minister, to respond what she called a "slap in the face for the Italian Government".

Sgrena, a veteran war correspondent who was held hostage for a month in Iraq, wrote: "After the apologies comes the slap in the face."

She said that the Americans had not listened to either her testimony or that of another Italian agent, even though, she said, both had given the same evidence without discussing what had happened.

"Obviously, our two testimonies given to the American commission were useless. Or will I be charged with perjury?" questioned the journalist.

"The greatest disappointment would be if our authorities were to accept this insult without reacting."

The US army official said that the US investigation concluded that "the soldiers were all complying with the standard operating procedures for those checkpoints and therefore were not culpable of dereliction of duty in following their procedures".

He added: "There is deep remorse over what happened. Everybody feels terrible about it. But given the climate and the security atmosphere, the security procedures in checkpoint operations have to be run by the letter."

Immediately after the March 4 incident, the US military said that the vehicle was approaching at a high rate of speed and failed to respond to hand signals, flashing white lights and warning shots. That version of events was disputed by Sgrena, who said the vehicle was travelling at a normal speed.

"I think there are problems determining what the rate of speed was. The reporter said they weren’t speeding. The US soldiers said it was. So there is disparity over the speed of the car," the official said.

Another key issue was whether the Italians had notified the Americans that Calipari would be traveling to the airport with Sgrena, and if so why the soldiers manning the checkpoint had not been alerted.

"I think there is disagreement over the communication aspect of it, of when somebody was told and what happened thereafter," the official said.

The Americans have offered to release the report, but Italy is blocking its publication while the Government works out its response.

The shooting has already strained US ties with Italy, one of Washington’s closest allies in Iraq, and triggered calls for Italy to pull out its troops.

Its 3,300-strong contingent in Iraq is the fourth largest after the United States, Britain and South Korea. Signor Berlusconi has promised to bring the troops home by the end of the year.

Richard Owen, Rome Correspondent of The Times, said that the Italian Government could refuse to counter-sign the report or could decide to issue their own report, since the official Italian version completely contradicts the Pentagon version of events.

"It comes a very bad time for Signor Berlusconi, just when he's reforming his Government after disastrous losses in regional election," Owen said.

"It will also increase pressure on him to withdraw Italian troops as soon as possible."

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