U.S.-led forces freed three Italian security contractors and a Polish businessman held captive at a hideout south of Baghdad on Tuesday, U.S. officials said. It was the first known military operation aimed at rescuing civilian hostages since insurgents began targeting foreigners for kidnapping in mid-April.

A new round of car bomb attacks on Tuesday killed at least 11 Iraqis and a U.S. soldier, the military said. In a separate incident, the Associated Press reported that six European soldiers -- two Poles, three Slovaks and a Latvian -- were killed when munitions they were carrying on a truck exploded on a road south of Baghdad.

One of the car bombs exploded outside city hall in Mosul, a Kurdish city in northern Iraq, killing nine Iraqis and injuring 25, the U.S. military said. Witnesses said three bombers in an orange-and-white taxi were responsible for the attack, which engulfed nine vehicles in flames.

City hall was not damaged, but other buildings in the immediate area had "significant damage," the military said. It said the attack apparently targeted two members of the Nineveh Provincial Council and the deputy police chief of Mosul. They were traveling in a convoy near city hall when the attack occurred, according to the military. The deputy police chief was wounded but not seriously. The council members were uninjured.

In Baqubah, about 30 miles northeast of Baghdad, a suicide attacker killed the U.S. soldier and at least two Iraqi civilians at a checkpoint outside the gate of the local military base. Ten soldiers and six Iraqi civilians were wounded. Soldiers were preparing to inspect the vehicle when the bomb exploded at around 8 a.m., the military reported.

Occupation officials and military commanders have predicted a surge in violence leading up to the formal handover of limited authority to an interim Iraqi government, set for June 30.

Lt. Gen. Ricardo Sanchez, commander of U.S. forces in Iraq, expressed confidence that the violence could be brought under control. "We're concentrating on the security situation here in Baghdad, and we've got the forces dedicated to ensure that we can improve that situation here in the city," he said at a news conference.

Reporting on the rescue of the hostages, Sanchez said no gunfire was exchanged and "several individuals" were detained. He declined to disclose the exact location of the operation and said more details would be released later.

The three freed Italians -- Umberto Cupertino, Maurizio Agliani and Salvatore Stefio -- were kidnapped on April 12 near Baghdad at the height of a wave of kidnappings aimed at foreigners. A fourth man, Fabrizio Quattrocchi, was killed by his captors. A videotape of the killing was made public, and his body was later returned to Italy.

The Polish civilian, Jerzy Kos, was seized June 1 from his company's offices in Baghdad.

Sanchez said the freed hostages were all in good health.

Top Polish and Italian diplomats in Iraq flanked Sanchez on Tuesday night as he announced the rescue.

"This is a great day for the released hostages, for the families, for Italy, for all of us," said Gianludovico de Martino, Italy's ambassador to Iraq.

Adam Wielgosz of Poland called the rescue a "very, very good example of the cooperation in the fight of terrorism also here in Iraq."

In a separate report, the Associated Press said that seven Turkish civilian contractors were in the hands of kidnappers, although it was not clear when they were taken. A videotape showed three of the hostages crouching on the floor in front of an Iraqi flag and holding their passports, opened to the photo page, the AP reported. The men were surrounded by others with their faces covered by scarves, two of them wielding assault rifles and another holding a rocket-propelled grenade. Four other hostages were shown separately, the AP reported.

"We urge the Muslim Turkish people . . . to stand by the side of their Iraqi Muslim brothers in their crisis by refusing to work with the occupation forces," said one of the masked men.

A U.S. soldier and two American civilians remain missing since an April 9 attack on a fuel convoy.

The soldier, Pfc. Keith M. Maupin of Batavia, Ohio, was last seen in an April 16 videotape. The civilians -- William Bradley of Chesterfield, N.H., and Timothy Bell of Mobile, Ala. -- have not been seen since the attack. Both were truck drivers for the Halliburton Co. subsidiary KBR.

Also on Tuesday, at least seven Iraqis were killed in clashes between U.S. forces and insurgents near the restive city of Fallujah, news services reported.