Abir Salim, the director of municipal services in the city which houses the mausoleums of two of Shiite Islam's most revered figures, was shot dead as he was carrying out his duties on Tuesday, Prime Minister Mustafa al-Kadhemi's office said.

He was on foot supervising a survey of unauthorised construction in Karbala when his killer pulled out a gun and shot him at close range.

Security camera footage posted on social media showed an attacker, dressed in a traditional white robe, open fire in the street and Salim fall to the ground.

The suspected killer was arrested shortly afterwards.

"Murderers and criminals will not escape punishment," the prime minister promised as he visited Karbala on Wednesday to offer his condolences to Salim's family.

His office released photographs of him berating the suspected killer, who had been blindfolded by his police captors, during a visit to the crime scene.

The images did little to assuage public anger at the apparent impunity for politically linked crimes that has seen more than 70 activists targeted for assassination since October 2019.

"The weakness of the security forces goes hand in hand with the intimidation of society by the tribes, religion and the political parties," one Twitter user complained.

Another demanded that Kadhemi show the same energy in tracking down the killers of pro-reform activists.

There have been no claims of responsibility for the wave of killings.

But supporters of anti-government protests that broke out in 2019 charge that the culprits are known to the security forces but allowed to go free because of political connections, particularly with Iraq's powerful neighbour Iran.

After decades of war, insurgency and sectarian conflict, Iraq has no shortage of firearms in circulation.

According to the Small Arms Survey, the country counted 7.6 million registered firearms in 2017 for a population of 39 million people, 40 percent of them under the age of 14. Many more are unregistered.