Gunmen have killed seven people including two aides to Ayatollah Ali al-Sistani, Iraq's highest Shi'ite authority and a key supporter of elections planned for later this month.
Al-Sistani aide Cleric Mahmoud al-Madaen was killed in Salman Pak, south of the capital, Baghdad.
His son and four guards were also killed.
Another aide working on legal issues in Ayatollah Sistani's office in the holy city of Najaf was also found dead.
Iraqi officials have accused Sunni Islamist militants of trying to provoke a civil war by killing prominent Shi'ites.
