Police said that Sheikh Hassan Mohammed Mahdi al-Jawadi, 56, was gunned down in front of his office by gunmen in a car on Sunday.

A police officer from Imara in Misan province said gunmen had also killed al-Jawadi's son, who was a policeman, two weeks ago in a similar attack.

Al-Jawadi's killing comes a day after Sistani warned Nuri al-Maliki, the Iraqi prime minister, of the dangers Iraq faced from militias if his fledgling government failed to curb the raging sectarian violence.

Maliki met Sistani in the holy city of Najaf following massive killings of Shia last week in and around Baghdad.