Iraq's cabinet clamped down on boycotting ministers from the Sunni-backed Iraqiya bloc by decreeing on Tuesday that they could not run their ministries while staying away from its meetings.

The reprisals were the latest escalation in a festering dispute between the Shiite-led government and Iraqiya that erupted last month as US troops completed their withdrawal from Iraq.

"The cabinet decided that boycotting ministers are not allowed to run their ministries and all their signed decisions are nullified," a statement from government spokesman Ali al-Dabbagh said.

Dabbagh said the cabinet had decided that ministers already nominated as temporary replacements on January 4 would take over the duties of their boycotting colleagues.

Since late December, Iraqiya has been largely boycotting parliament and the cabinet in protest at what they say is Prime Minister Nuri al-Maliki's centralisation of power.

The bloc, which holds 82 seats in the 325-member parlaiment, has not pulled out its nine cabinet ministers, however.

Although Maliki had originally threatened to fire ministers who failed to attend cabinet, he later backed off and handed their portfolios to other ministers on a temporary basis.

The row erupted when authorities charged Sunni Arab Vice President and senior Iraqiya leader Tareq al-Hashemi with running a death squad shortly after the December 18 withdrawal of US forces.

Maliki, a Shiite, also called for Sunni deputy premier Saleh al-Mutlak to be sacked after he called the prime minister a dictator "worse than Saddam Hussein."

Hashemi, who denies the charges, has been holed up in the autonomous Kurdish region for the duration of the crisis and Kurdish officials have so far declined to hand him over to Baghdad.

The United Nations and the United States have urged calm but their calls for talks involving all of Iraq's political leaders have so far gone unheeded.