The attack occurred about 8:30 p.m. in the center of Tal Afar, according to Col. Abdul-Karim Mohammed of the Nineveh provincial police, who gave the casualty figures. The director of the city hospital, Saleh Qado, said 20 people were killed and 70 injured.
Officials said the blast occurred near closing time as people packed the market to finish their shopping. Qado said U.S. medics were providing first aid to the injured on the scene before they were transported to his hospital.
Lt. Col. Ali Rasheed of Iraq's Interior Ministry said the death toll was between 15 and 20 and the attack occurred near a police station within the market area.
In March, President Bush cited Tal Afar, a mostly Turkomen city 260 miles northwest of Baghdad, as a success story after U.S. troops regained control there last year.
U.S. and Iraqi forces launched an operation in September aimed at cleansing the city of insurgents, the second such attempt in a year.
In other developments:
However, by the end of September, a woman suicide bomber slipped into a crowd of recruits, killing at least six people and wounding 30.
Since then, the city has been hit by several suicide attacks. In October, a suicide bomber plowed his explosives-packed vehicle into a crowded outdoor market, killing 30 and wounding 45.
In March, another suicide bomber struck a joint U.S.-Iraqi military base near the city, killing at least 15 and wounding as many as 30.
A month later at least six people were killed in the city in another suicide attack.
In addition to the suicide attack Tuesday, in other violence, two drive-by shootings killed four Iraqis in Baghdad, including Raad Mohammed al-Dulaimi, a member of the Iraqi Islamic Party, a major Sunni Arab political party. A roadside bomb also hit a police car in Baghdad, killing one officer and wounding two.
The bodies of 17 Iraqis were found: five in the capital; one in northern Iraq; eight, including a 10-year-old boy, in a river 30 miles south of Baghdad; and three Interior Ministry police commandos in Mahawil, 45 miles south of the capital.
They all appeared to be victims of sectarian death squads that have kidnapped and killed hundreds of Shiites and Sunnis in the last few months and dumped their bodies on city streets or in remote areas. Insurgents sometimes carry out such killings to punish Iraqis who are working for Iraq's military, police forces or government.