Abdel Mehdi al-Karbalai, the representative of Grand Ayatollah Ali Sistani, issued the call during weekly Friday prayers in the holy city of Karbala.

He said Iraqis who will vote in the May 12 polls should not re-elect candidates from among MPs and officials who have already held government jobs and proved to be "corrupt and failing".

Iraq is ranked the 12th most corrupt country in the world by Transparency International.

More than 24 million Iraqis are registered to elect 320 deputies from a field of around 7,000 candidates on May 12, with 71 seats reserved for the capital.

According to the electoral commission, only 20 percent of the candidates are newcomers.

Karbalai said voters should "avoid falling into the trap of those who want to fool you", including "those whom you have known" -- a reference to outgoing MPs and other officials running in the polls.

Political analyst Aziz Jaber said Karbalai's remarks targeted "heads of lists who have held government jobs and MPs such as vice-presidents Nuri al-Maliki and Ayad Allawi".

Prime Minister Haider al-Abadi -- accused by critics of failing to tackle rampant corruption in Iraq -- heads one of the main lists and hopes to be re-elected.

Shiite religious parties have come to play a greater role in the years since the 2003 US-led invasion that toppled dictator Saddam Hussein.

Sistani, whose opinions are widely respected among Shiites, mobilised tens of thousands of men to join paramilitary units of the Hashed al-Shaabi, which played a crucial role in defeating the Islamic State group in Iraq.