Two truck bombs struck markets in Tal Afar on Tuesday, killing at least 66 people, and suspected Sunni insurgents tried to ambush ambulances carrying the dozens of wounded in the second attack on the predominantly Shiite city in four days. The bombings highlighted the resurgent violence in a city US President George W. Bush held out as a symbol of US success a year ago. The deadliest blast occurred when an explosives-laden trucks was detonated by remote control while people gathered to buy the flour it was carrying in a Shiite neighborhood in the center of the city, 420 kilometers northwest of Baghdad. At least 62 people were killed and 150 wounded in that attack, which occurred about five minutes after a truck loaded with vegetables blew up near a wholesale market in a northern part of the city, killing one person and wounding four, provincial police spokesman Brig. Abdul Karim al-Jubouri said. Insurgents waiting in cars on the city's outskirts then tried to intercept ambulances carrying the wounded to hospitals in nearby Mosul but fled after police escorts opened fire, according to Husham al-Hamdani, head of the security committee in Mosul. Jaafar Akram, a teacher at a nearby school who saw the first explosion, said body parts were thrown on the ground and the walls and vegetables were scattered in pools of blood. "I instantly saw smoke then I heard the blast," Akram said. "Thanks be to God the blast didn't occur during rush hour at the school. That reduced the disaster." 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, about 150 kilometers east of the Syrian border, is a mainly Turkomen city with about 60 percent of its residents adhering to Shiite Islam and 40 percent Sunnis It has suffered frequent insurgent attacks, but Tuesday's was the deadliest since the war started more than four years ago. Among the largest previous attacks were suicide bombings that killed 20 on Sept. 18, 2006, and 30 in an attack outside an army recruiting center on Oct. 11, 2005. Tal Afar was an insurgent stronghold until US and Iraqi troops drove them out in a September 2006 operation and constructed huge sand barriers around the city to limit access. On March 20, 2006, US President George W. Bush cited that operation, in which insurgents melted away into the countryside rather than fight, as an example that gave him "confidence in our strategy." A suicide car bomber also exploded his payload 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 other 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 a US-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. The total number of people killed by car bombs in Baghdad has decreased to at least 349 since the security operation started, compared with 525 in the previous six weeks. Car bombs outside the capital, meanwhile, killed at least 100 Iraqis in the six weeks leading up to the crackdown, but have more than doubled to at least 233 Iraqis killed since the security sweep was launched, including those who died in Tuesday's attacks. The capital faced fresh attacks on Tuesday as well. Mortar rounds slammed into a Shiite enclave in the Sunni-dominated Dora neighborhood in southern Baghdad, 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 center of the capital at about 5:40 p.m., but he was able to detonate his explosives killing one policeman and seriously wounding three other people, police said. And an explosion struck the heavily fortified Green Zone, which is home to the US and British embassies and thousands of American soldiers, US Embassy spokesman Lou Fintor said. He had no word on casualties. Police reported a total of 80 people killed or found dead nationwide, including two elderly sisters who were both Chaldean Catholic nuns who were stabbed multiple times by intruders who raided their home Monday night near the Cathedral of the Virgin in the northern city Kirkuk. They lived alone and there was no sign of a robbery. Police 1st. Lt. Marewan Salih said the nuns - 79-year-old Margaret Naoum and 85-year-old Fawzeiyah Naoum, 85 - lived alone and there was no sign of a robbery. Naoum was stabbed seven times as she stood in the garden just outside the sisters' home, 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.