Italy paid homage Monday to an intelligence officer killed by U.S. fire in Iraq while escorting an ex-hostage to freedom, with a state funeral in a Rome basilica drawing as many as 20,000 mourners — some bringing flowers, some waving flags — and all of the country's top officials.

The killing of Nicola Calipari (search), 50, fueled anti-American sentiment in a country that was strongly opposed to the war in Iraq, and prompted Premier Silvio Berlusconi (search), a staunch supporter of the U.S.-led military campaign, to demand that Washington provide a full explanation of the shooting in Baghdad.

"A grateful and admiring Italy bows to its hero, the victim of a war without a name," said the Vatican newspaper, L'Osservatore Romano, which opposed the Iraq war. "His gesture has moved the whole country."

The Santa Maria degli Angeli basilica — originally designed by Michelangelo (search) on the ruins of the Baths of Diocletian — and the surrounding piazza were packed with mourners. Berlusconi and U.S. Ambassador Mel Sembler were among dignitaries at the service.

An honor guard slowly carried the casket draped with the tricolor Italian flag into the church. In the front row, Calipari's relatives — his wife Rosa and his children Silvia, 19, and Filippo, 14 — gripped each other's hands and dabbed away tears. Several buried their faces in their hands.

Applause broke out when the casket arrived and when it was carried out of the church after the 90-minute funeral, which was broadcast live on several Italian television channels as well as on the Vatican's CTV, which usually limits coverage to Vatican ceremonies.

Before the funeral, Calipari's body lay in state at Rome's Vittoriano monument, where police estimated 100,000 people streamed past his coffin. The body had been returned from Iraq on Saturday night.

Calipari was shot as he headed to Baghdad airport after securing the release of Giuliana Sgrena, an Italian journalist who had been held captive for a month after her Feb. 4 abduction in Baghdad. He died instantly from a bullet to his head, according to an autopsy. Sgrena said he died while trying to shield her with his body from the American fire.

Sgrena, who was recovering in a Rome hospital from a shrapnel wound in the shoulder, did not attend the funeral, but her brother, companion and many colleagues at her paper, the communist daily Il Manifesto, did.

"We almost feel guilty for what happened," Sgrena's brother, Ivan, said after the service.

Adding to the pain of the nation was a feeling of frustration as details of the shooting remain sketchy.

"He gave his life to our country. He died fulfilling his duties. He deserves great respect and memory," said Alessandro Lazari, a bank officer at the funeral. "The circumstances of his death are really ambiguous. I hope that the truth will come out as soon as possible."

Italian military officials said two other intelligence agents were wounded in the shooting; U.S. officials said it was only one. Sgrena rejected the U.S. military's account of the shooting, claiming that American soldiers gave no warning before they opened fire.

In remarks published this week, Sgrena also said that it was possible they were targeted deliberately because the United States opposes Italy's policy of negotiating with kidnappers. She did not offer evidence to sustain her statement, and Rome prosecutors Franco Ionta and Pietro Saviotti, who are investigating the killing, said that there's no evidence indicating the shooting was the result of an ambush, according to news reports.

The White House dismissed Sgrena's claim as "absurd."

"It's absurd to make any such suggestion, that our men and women in uniform would target individual citizens," White House press secretary Scott McClellan said. He noted that the car was traveling on one of the most dangerous roads in Iraq.

Washington has promised to shed light on the shooting, which White House counselor Dan Bartlett described in an interview with CNN as a "horrific accident." On Friday President Bush called Berlusconi to offer his apology and pledge a full investigation.

The U.S. ambassador, who was summoned to the premier's office in the hours immediately after Calipari's death, was back there again Monday evening for another meeting with Berlusconi, state TV reported. Also at the meeting was Foreign Minister Gianfranco Fini, the station reported.

The killing has fueled anti-American sentiment in Italy, a country where Bush is unpopular and where tens of thousands have taken to the streets to protest the war and Berlusconi's decision to send 3,000 troops after Saddam Hussein's ouster.

At the funeral, officials said this was a time for national unity.

"This is the moment to pay homage all together, without controversy, to the heroic gesture of Nicola Calipari," Berlusconi's right-hand man, Gianni Letta, told the crowd. "We are proud of you, we'll follow your example and your extraordinary lesson in life."

Condolences also came from abroad. French President Jacques Chirac, who opposed the war, expressed his "full solidarity," while in Brussels the European Commission expressed regret for the "unfortunate accident" that cost Calipari his life.