The nation was shaken: Italians left flowers for the fallen troops outside the headquarters of the Carabinieri paramilitary police, while at Rome's tomb of the unknown soldier, Italy's green-white-and-red flag rippled at half staff. In parliament, lawmakers held a minute of silence.
Italian Premier Silvio Berlusconi pledged that Italy would not be discouraged from its mission in Iraq. But opposition leaders - offering strong condolences at a time of national mourning - hinted there would be questions later about the direction of the U.S.-led occupation.
Other Italians expressed horror.
"They go in thinking they can help bring peace, but they end up dead," said 26-year-old Silvano Larice. "It's not right. It makes no sense."
Berlusconi told lawmakers in parliament: "The feeling of the nation at this moment is pain."
The premier described this as "a day in which political bickering should go silent."
The heated debates that usually mark Italian politics were muted Wednesday. But that was not likely to last.
"Today isn't the time for a critical reflection," center-left opposition leader Francesco Rutelli said. "That will have to be done in the coming days, considering the Italian presence, the purpose of the mission, the need for a U.N. command and to not leave Iraq at the mercy of terrorism."
Before the war, opinion polls showed a majority of Italians opposed the conflict. In February, during a day of global anti-war demonstrations, Rome drew the world's single biggest rally, with about 1 million Italians marching.
Still, the conservative Berlusconi supported the U.S.-led campaign in Iraq, establishing himself as one of President Bush's closest allies in Europe. Italy did not send combat troops, instead dispatching a 2,500-strong contingent to help rebuild the country after Saddam Hussein's regime fell.
On Wednesday morning, that mission was darkened by violence.
An explosive-laden truck approached a building at the Italian compound in the southern city of Nasiriyah. Guards returned fire, but the vehicle plowed through the gate and exploded.
The catastrophe came despite Italy's determination since World War II to avoid the sort of military disasters suffered under Fascist dictator Benito Mussolini. Today, few Italians consider their military a fierce fighting force, and the country has recast its armed forces overseas as peacekeepers.
Twelve of the dead Wednesday were Carabinieri paramilitary police. Four army soldiers were also killed as well as an Italian civilian, an Italian documentary filmmaker, and at least eight Iraqis.
As wreaths piled up around the Carabinieri headquarters in Rome, some Italians said they had doubts about the mission in Iraq.
"It's not clear what is happening anymore in Iraq," said Debora Tarolla, a 34-year-old archaeologist. "It's not a war, but we don't seem to be rebuilding anything either."
Messages of sympathy poured in from around the world.
Pope John Paul II said: "I express my firmest condemnation of this new act of violence that, added with other cruel gestures carried out in that tormented country, does not help pacification or renewal."
At the White House, President Bush offered his condolences.
"Today in Iraq, a member of NATO - Italy - lost some proud sons in the service of freedom and peace," he said. He thanked grieving families for their sacrifices and added, "I appreciate the steadfast leadership of Prime Minister Berlusconi, who refuses to yield in the face of terror."
It was an unusual statement for Bush, who has not paid such personal tributes to fallen American soldiers. In the past, he has said the United States mourns all slain troops, without tying the remarks to specific incidents.
The last time Italy suffered military losses near this level was in 1961, when 13 Italian airmen were killed in Congo during an aid operation. Italy also lost two aircraft in separate incidents in the former Yugoslavia, leaving four dead on each occasion.
"We go to bring peace, and we're repaid in this way," said Gen. Serafino Liberati, the head of the Carabinieri.
"We have eyes swollen with tears. We have hearts full of anger."
By Tom Rachman