ROME - Italy and the United States said Friday the investigation into the killing of an Italian agent by U.S. forces in Iraq had ended but they failed to fully agree on the circumstances surrounding the shooting.

The two governments issued a joint statement into the March 4 death of intelligence agent Nicola Calipari, who was killed after he had secured the release of an Italian hostage. U.S. soldiers fired on their vehicle as it approached a U.S. checkpoint near Baghdad's airport.

It said the investigation into the shooting had been concluded and the two countries will now refer the case to their respective national authorities. Italy has launched its own criminal inquiry into the death. "The investigators were unable to reach shared final conclusions..."

Italy and the United States had worked for a month on the joint investigation in the killing, which sparked outrage in Italy and put increasing pressure on Premier Silvio Berlusconi to withdraw Italy's estimated 3,000-strong contingent from Iraq.

But from the start, testimony from the two survivors of the shooting clashed with the U.S. military's account.