BAGHDAD (AP) – Two truck bombs shattered markets in Tal Afar on Tuesday, killing at least 63 people and wounding dozens in the second assault in four days on a predominantly Shiite Muslim city hit by a resurgence in violence a year after it was held up as a symbol of U.S. success.

After the bombings, suspected Sunni insurgents tried to ambush ambulances carrying the injured out of the northwestern city but were driven off by police gunfire, Iraqi authorities said.

A major Sunni Arab insurgent group reported its military leader was slain outside Baghdad, an assault likely to deepen an increasingly bloody rift between al-Qaida in Iraq and opponents of the terror group in Sunni communities west of the capital.

In Baghdad, a U.S. soldier and an American working as a U.S. government contractor were killed by a rocket attack on the heavily guarded Green Zone, U.S. officials said. Another contract worker suffered serious wounds and three were slightly wounded.

U.S. soldiers, meanwhile, foiled two suicide truck bombings aimed at their base in a small town 50 miles west of Baghdad and killed as many as 15 attackers, the military reported. It said eight soldiers suffered wounds, all but one of them slight, during the firefight in Karmah.

Iraqi police reported at least 109 people killed or found dead nationwide. The toll included two elderly sisters – both Chaldean Catholic nuns in the increasingly tense city of Kirkuk – who were stabbed multiple times in what appeared to be a sectarian killing.

Most of the bloodshed in Tal Afar came when an explosives-laden truck was detonated by remote control as people gathered to buy flour it was carrying in the center of town, 260 miles northwest of Baghdad. A few minutes earlier, a truck loaded with vegetables blew up near a wholesale market on the city’s north side.

Brig. Abdul Karim al-Jubouri, a spokesman for the provincial police, said the first blast killed at least 62 people and wounded 150. The other bomb killed one person and wounded four, he said.

On Saturday, a man wearing an explosives belt blew himself up outside a pastry shop in Tal Afar’s central market area, killing at least 10 people and wounding three.

Tal Afar, which is about 90 miles east of the Syrian border, is inhabited mainly by ethnic Turkomen. About 60 percent of the residents are Shiite Muslims and the rest Sunni.

The city was an insurgent stronghold until an offensive by U.S. and Iraqi troops in September 2005, when rebel fighters fled into the countryside without a battle. Last March, President Bush cited the operation as an example that gave him “confidence in our strategy.”

But even though U.S. and Iraqi forces put up sand barriers around Tal Afar to limit access, the city has suffered frequent insurgent attacks – Tuesday’s was the deadliest since the war started. Among the largest previous attacks were suicide bombings that killed 20 people on Sept. 18 and 30 on Oct. 11, 2005.

In other bomb attacks Tuesday, a suicide car bomber struck northeast of Ramadi in a district not patrolled by the military, killing 10 people, police Col. Tarik Yousif said. Another attacker detonated his explosives-laden car near a police patrol in Baqouba, northeast of Baghdad, killing two policemen and wounding four people, police said.

The vehicle bombings and an outbreak of sectarian clashes in southern Iraq underscored concerns that militants have fled the capital in response to the U.S.-led security crackdown, bringing violence with them to the hinterlands.

Nationwide, the number of deaths from car bombs has decreased slightly since the Baghdad security operation began Feb. 14, but it has more than doubled in areas outside the capital, according to an Associated Press tally.

Car bombs killed at least 349 people in Baghdad in the six weeks since the crackdown began, down from 525 such deaths in the preceding six weeks. But the numbers killed by car bombs outside the capital jumped from at least 100 in the earlier period to at least 233 in the latest six weeks.

In an interview with CNBC, Lt. Gen. Ray Odierno, a top U.S. commander in Iraq, said it was too early to say how long the expanded U.S. troop presence accompanying the Baghdad operation will be needed. He said it depended on how soon Iraqi forces can take on all responsibility for security.

“I believe that within five to six to eight months, we’ll be able to make a good assessment of where they are in building their capacity, and based on that, we’ll be able to make a decision on how long this surge will go,” he said.

The Sunni insurgent group known as 1920 Revolution Brigades said its military leader, Harith Dhaher al-Dhari, was killed in Abu Ghraib just west of Baghdad. An Iraqi district official said attackers fired rocket-propelled grenades at the man’s car, but the U.S. military said suicide car bombers attacked his house.

The attack came as the Shiite-led government of Prime Minister Nouri al-Maliki is reportedly making progress rallying Sunni Arab tribesmen into joining the fight against al-Qaida members in Anbar province west of the capital. Al-Dhari’s group is among those rumored to be taking part in secret talks with the government.

Al-Qaida has responded with bomb attacks targeting leaders and key supporters of the tribes allied against them.

In the northern city of Kirkuk, police 1st Lt. Marewan Salih said the slain nuns – 79-year-old Margaret Naoum and 85-year-old Fawzeiyah Naoum, 85 – were killed in their home near the Cathedral of the Virgin. They lived alone and there was no sign of a robbery, he said.

Naoum was stabbed seven times as she stood in the garden just outside the house, while Naoum was stabbed three times while lying on the sofa inside as she was recovering from eye surgery last week.

Chaldean Catholics are an ancient Eastern rite now united with Roman Catholicism. Adherents live mainly in Syria, Turkey, Iran and Iraq and most speak a dialect of Turkish.

In Baghdad, U.S. Charge d’Affairs Daniel Speckhard said a rocket attack killed an American contract worker in the Green Zone, the heavily fortified area that is home to the U.S. Embassy and Iraqi government offices. The U.S. military said an American soldier also was killed.

Speckhard, standing in as U.S. ambassador since Zalmay Khalilzad left Monday, did not release the victim’s name. U.S. officials also did not give the nationalities of the four wounded workers.

Elsewhere in the capital, mortar rounds slammed into a Shiite Muslim enclave in the Sunni Arab-dominated Dora neighborhood, killing four people, including two children – the second deadly mortar attack on the area in three days.

Police also opened fire on a suicide car bomber as he drove toward a checkpoint near a cemetery in the city center, but he was able to set off his explosives and killed one officer while seriously wounding three people, police said.

—

AP News Research Center in New York contributed to this report.

AP-ES-03-27-07 1759EDT