After gunmen assassinated a prominent Iraqi security researcher, Hisham al-Hashemi, in Baghdad, Iraqi Prime Minister Mustafa al-Kazemi vowed, on Tuesday, the perpetrators to pay the price.

"we will never allow chaos and mafia policy," Al-Kazimi said in tweets via the Prime Minister's media office account on Twitter.

He said that Iraq "will not sleep until the killers submit to the judiciary, on the crimes they committed."

Al-Hashemi, known for his sharp criticism of the militia’s hegemony, was assassinated in Baghdad on Monday, after receiving threats from the spokesman for the Hezbollah Brigades Abu Ali al-Askari.

The killing of al-Hashemi shocked the Iraqis, and condemnation from the United States, Britain, and the United Nations Mission in Iraq.