Nasiriyah, Iraq ? A suicide bomber blew up a truck packed with explosives at an Italian paramilitary base Wednesday, killing at least 26 people. The United States struck at the Iraqi insurgency hours later, destroying a warehouse in Baghdad and chasing attackers who were seen firing mortars.

The Nasiriyah attack was the deadliest against an American ally since the occupation began and appeared to send a message that international groups are not safe anywhere in Iraq. It came on the same day the chief U.S. administrator for Iraq went to the White House to put forth proposals on transferring more authority to the Iraqis.

Col. Gianfranco Scalas said 18 Italians were killed: 12 Carabinieri paramilitary police, four soldiers, a civilian working at the base and a documentary filmmaker. A spokesman for the U.S.-led coalition said at least eight Iraqis also died. The bomber — whose nationality was not known — also died.

The blast wounded about 80 people, 20 of them Italians, hospital sources and Italian officials said.

Italians were stunned by their nation’s single worst military loss since World War II and its first in the Iraq campaign. At Rome’s tomb of the unknown soldier, the green-white-and-red flag rippled at half-staff, and parliament had a minute of silence.

Italian Premier Silvio Berlusconi pledged that Italy’s mission in Iraq would not be derailed. Opposition leaders who opposed the deployment to postwar Iraq called on the government to withdraw the contingent.

There were conflicting accounts of the attack, which took place about 10:40 a.m. at a three-story building used by the Carabinieri’s multinational specialist unit in Nasiriyah, 180 miles southeast of Baghdad.

Witnesses said the decoy car ran a roadblock in front of a square where the Italian barracks was located. Guards opened fire but as the vehicle sped away, the fuel tanker approached from the opposite direction and rammed into the gate of the building before exploding.

U.S. retaliates

An Iraqi boy recuperates in a hospital after he was injured in the suicide truck bomb attack against Italy's paramilitary police headquarters in Nasiriyah, Iraq. At least 26 people were killed in the attack Wednesday.

After nightfall in Baghdad, forces from the 1st Armored Division attacked a warehouse used by insurgents, setting off explosions that reverberated through the capital.

The mission was part of “Operation Iron Hammer,” a new “get tough” policy for confronting insurgents.

Also Wednesday, troops in Baghdad spotted attackers firing mortars, a statement from the 1st Armored Division said. The attackers fled in a van, making several stops as they tried to evade pursuing ground troops.

White House strategy

From the White House, President Bush on Wednesday directed his top official in Baghdad to push new options to speed the transfer of power to the Iraqi people.

The president sent U.S. administrator Paul Bremer back to Baghdad with new proposals for a quicker power transfer, perhaps through the establishment of an interim government that would be drawn from the 24-member Iraqi Governing Council, according to administration officials.

One idea floated by the administration called for empowering a smaller group within the council or perhaps elevating a single strong council leader to the chief position of authority, similar to the power structure set up after the fall of the Taliban in Afghanistan. Under another proposal, Iraq would have some form of elections within six months.

Flowers are placed in front of the Carabinieri headquarters in Rome. The tribute was left in memory of Italian soldiers and Carabinieri police killed in a truck bomb attack Wednesday in Iraq.