MICHAEL PROBST/AP

An unidentified casualty is stretchered into an ambulance at the U.S. Airbase of Ramstein, southern Germany, on Wednesday. Some 50 patients, most of whom were injured during Tuesday's attack in Mosul, Iraq, arrived at Ramstein Air Base on Wednesday.

By the Associated Press

BAGHDAD, Iraq - The U.S. military said Wednesday that a suicide bomber likely carried out the explosion at a U.S. base near Mosul, spraying a crowded mess tent with small pellets and killing 22 people - nearly all of them Americans.

The apparent sophistication of Tuesday's operation - the deadliest single attack on U.S. troops since the war began - indicated the attacker probably had inside knowledge of the base's layout and the soldiers' schedule. The blast came at lunchtime.

Other developments in Iraq on Wednesday:

- There was little apparent sympathy for the dead Americans on Mosul's deserted streets, where hundreds of U.S. troops, backed up by armored vehicles and helicopters, blocked bridges and cordoned off Sunni Muslim areas of Iraq's third-largest city.

- About 50 people - most of them injured soldiers from Mosul - arrived in Germany aboard an Air Force C-141 transport plane. As a light snow fell, some wounded were carried away on stretchers.

- Four Iraqi civilians from one family were killed and three others were injured when U.S. soldiers opened fire on their car in the Abu Ghraib area just west of Baghdad, said Akram Al-Zaobaie, a doctor in the local hospital. The seven were traveling in a taxi when a roadside bomb hit an American military convoy, he said.

- Polish Prime Minister Marek Belka toured Camp Echo in Diwaniyah, the new headquarters for the Polish-led international security force in central Iraq, on a Christmas visit to some 2,400 Polish troops stationed in Iraq.

- In the town of Mahmoudiyah, 25 miles south of Baghdad, a gas tanker exploded, killing four people and injuring about 50. Witnesses said the tanker was hit by a rocket.

- In the town of Latifiyah, 20 miles south of Baghdad, a suicide bomber detonated his car against a checkpoint, killing three Iraqi National guardsmen, police officials said.

- Two French journalists freed from captivity in Iraq arrived home to a tearful welcome from their families, ending a four-month drama that had gripped France.

- The growing insurgency against U.S. forces in Iraq is fed by nationalist feelings and widespread distrust of the United States, the private International Crisis Group said. Challenging the Bush administration, the crisis group said, "The insurgency is not confined to a finite number of fanatics isolated from the population and opposed to a democratic Iraq."

- An international construction company has pulled out of its contract to rebuild Iraq's transportation systems, deciding it was too dangerous to stay, a spokesman for the U.S.-led reconstruction effort said. Contrack International Inc., which led a coalition of firms working on a $325 million contract to rebuild Iraq's roads, bridges and railways, withdrew from that contract last month after a surge in attacks on reconstruction efforts.

- All four water purification plants in Fallujah are still not working after last month's U.S.-led offensive that left the city in ruins, a Red Cross spokesman said, complicating life for displaced families when they return.