BAGHDAD, March 5: Italian journalist Giuliana Sgrena was freed by her captors on Friday but suffered severe wounds when US forces opened fire on the convoy taking her to Baghdad airport for the flight to Rome.

An Italian secret service agent accompanying the journalist was killed as he tried to protect Ms Sgrena. All three other passengers were wounded. Ms Sgrena was treated for a shrapnel wound in her shoulder at a US military hospital in Baghdad before boarding the plane.

The US military said American soldiers had tried to warn occupants of the vehicle - flashing lights and firing warning shots - as it sped towards a checkpoint, then fired into its engine block when it did not stop.

Italian Prime Minister Silvio Berlusconi was faced with one of the toughest moments of his rule as the incident infuriated a nation already embittered over his support to the US-led invasion of Iraq.

Mr Berlusconi immediately summoned the American ambassador, demanding explanations and declaring someone had to take responsibility. "We were turned to stone when the officials told us about it on the telephone," Mr Berlusconi said in a statement.

"The agent, Nicola Calipari, covered Sgrena with his body, he was hit by a bullet which unfortunately was fatal," he said.

US President George Bush called the Italian premier to express regret over the incident.

Mr Bush called Mr Berlusconi from the presidential jet, Air Force One, "to express his regret about the incident that occurred earlier today," White House spokesman Scott McClellan said.

"The president assured Prime Minister Berlusconi that the incident will be fully investigated," Mr McClellan said, adding that the two spoke for about five minutes.

Journalist Giuliana Sgrena "was fired upon by coalition forces. Apparently there was the loss of one life, an Italian citizen, and she was also injured in the incident," Mr McClellan said.

"We regret the loss of life, the Italian citizen who lost his life, and obviously she is in our thoughts and prayers as well."

The 57-year-old Sgrena was kidnapped on Feb 4. Guerillas later released a video of her sobbing and wringing her hands as she pleaded for Italian troops to leave Iraq.

NEW VIDEO: In a new video aired on Al Jazeera on Friday, Ms Sgrena was shown wearing a black dress and sitting in front of a table with a plate of fruit. Jazeera said that on the tape, Ms Sgrena thanked her captors for treating her well.