"We shall use an iron fist against the leaders of the gangs or those who threaten security," al-Maliki said in a speech. "And we shall ask all security departments to draw up an effective and quick plan to achieve security."
Violence has been increasing in the Shiite-dominated city with mostly Sunnis but some Shiites and police among the 140 killed in May.
Two British soldiers were killed in a roadside bombing in Basra on Sunday, bringing to nine the number of British personnel who have died in the city in May.
Al-Maliki, himself a Shiite, declared a monthlong state of emergency and denounced the violence that Sunni religious leaders are blaming on Shiite death squads, reported the Associated Press. He was meeting with religious leaders, city officials and others in an attempt to "heal the rift and find a solution for what caused the latest events in Basra."
Meanwhile, a car bomb in the northern city of Mosul struck a police patrol, killing at least five policemen and wounding 14.
In Baghdad, gunmen killed a Shiite prayer leader as he was leaving his home to go to the Imam Ali Mosque, police Capt. Ali Hussein said.
He also said Jamal Kadhim Hassoun al-Zamili, a former governor of Diwaniyah -- a town south of Baghdad, was killed in a drive-by shooting late Tuesday.
In Muqdadiyah, about 60 miles north of Baghdad, a bomb hidden in an air conditioner exploded and killed Mayor Sheik Allaywi Farhan al-Dulaimi, a member of the Sunni Iraqi Islamic Party.
Also, at least 19 bodies were found in separate locations in Baghdad, many blindfolded and handcuffed, apparent victims of sectarian violence often blamed on militias, according to the AP.
The latest violence came a day after car bombs ripped through a car dealership in a Shiite area in southern Iraq and a busy outdoor market north of Baghdad and other attacks killed 54 people and injured 120 nationwide.