Violence killed at least 29 people Sunday, including three American soldiers, and mortar fire rumbled through the heart of Baghdad after sundown despite stringent security measures imposed after an explosion of sectarian violence. A ban on driving in Baghdad and its suburbs helped prevent major attacks during daylight Sunday, but after nightfall explosions thundered through the city as mortar shells slammed into a Shi'ite quarter in southwestern Baghdad, killing 16 people and wounding 53, police said. Mortar fire also hit a Shi'ite area on the capital's east side, killing three people and injuring six, police reported. Nevertheless, officials announced they would let vehicles back on the streets at 6 a.m. Monday - in part because shops were running out of food and other basic supplies. Gasoline stations were closed, and people were unable to go to work Sunday, a workday in this Muslim country.