The slain, he added, included clerics, worshippers and others. The latest was a 70-year-old grocer who was shot dead by gunmen while standing in his store Monday night. A police officer in the city confirmed the 17 killings, speaking anonymously as he was not authorized to talk to media.
Khazrachi said the mosque closure was intended to protect Sunnis but was "also a message to all those in charge of the security to shoulder their responsibilities."
Basra is Iraq's second-largest city. It was controlled by militias for years before the U.S.-backed Iraqi army gained control following a series of offensives in 2008.
In Baghdad, meanwhile, a wave of car bombs hit commercial districts.
One blast struck the northeastern suburb of Husseiniya in the late afternoon, killing five people and wounding 14 others.
Shortly before sunset, another bomb went off near a juice shop in central Baghdad, killing three and wounding 21.
Two more died in another car bomb explosion near a restaurant downtown, and in western Baghdad, two blasts killed six people and wounded 20 others.
A final two blasts hit a commercial street in the capital's southeast, killing seven and wounding 71.
In the western city of Fallujah, security forces foiled an assault on a police station, killing four attackers. Two policemen were killed, officials said.
And in the northern city of Mosul, gunmen stopped a mini-bus carrying soldiers to their base, killing six with shots in the head, police said.
Medical officials confirmed the casualty figures. All spoke anonymously as they weren't authorized to release information.
Violence in Iraq surged in April after government troops moved against a camp of Sunni demonstrators in the town of Hawija north of Baghdad, triggering deadly clashes.
More than 4,000 people have been killed, including 804 just in August, according to United Nations figures. The monthly death tolls are the highest since 2008.
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Associated Press writers Sinan Salaheddin in Baghdad and Nabil al-Jurani in Basra contributed to this report.