He was speaking a day after announcing the country’s first democratically elected Government at the end of five months of factional negotiations. It came on a weekend in which there were more than 50 deaths in attacks as feuding Shia and Sunni politicians struggled to unite for the sake of their country.

Mr al-Maliki told reporters after the Cabinet’s first meeting yesterday: “We cannot imagine stability and security in this country with the existence of the militias who kill for their special interests.”

He had promised to restore security, root out corruption and promote reconciliation between Iraq’s ascendant Shia majority and one-time Sunni elite. The former Shia hardliner said he would rein in the Shia militias that have been linked to the Interior Ministry and are blamed for the deaths of thousands of Sunnis.

The formation of the national unity Government was hailed by President Bush as “a new day for the millions of Iraqis who want to live in peace”. He said: “I fully understand that a free Iraq will be an important ally on the War on Terror, will serve as a devastating defeat for the terrorists and al-Qaeda and will serve as an example for others in the region who desire to be free.”

Margaret Beckett, the Foreign Secretary, quashed hopes of a swift withdrawal of British troops, adding that allied forces would be needed for “quite a while”. First reports of the new Iraq Government raised hopes of an early withdrawal for the 140,000 US and British troops, but Mrs Beckett said that they would remain as long as they were needed.

“We are making some progress in both training and putting into place an Iraqi army, an Iraqi police force, who will increasingly take over some of these responsibilities,” she said on the Sunday AM programme on BBC One, “but I would envisage that even when responsibility is handed over to those Iraqi forces, they will probably want some outside support for quite a while.”

Mr al-Maliki’s determination to clamp down on militias marks a break from his Dawa party’s close ties with them and his past as a clandestine fighter against Saddam Hussein’s regime. “Weapons should be in the hands of government,” he said. “The militias and death squads are irregular and extraordinary.”

The filling of the Interior and Defence posts is critical to fighting the three-year Sunni insurgency and stopping the Shia death squads operating from inside the Interior Ministry.

Mistrust abounds between the Shia and Sunni political blocs, who failed to reach agreement on the two influential posts before Saturday’s parliament session. A dozen Sunni MPs walked out before the vote on the rest of the Cabinet.

The Sunni National Accord Front, with 44 seats, has drafted a list of candidates for Defence Minister, and the 128-seat Shia majority bloc has compiled names for the Interior Ministry, but they have failed to strike a deal. Frontrunners for the Interior Ministry were said to be the current national security adviser, Muawaffaq al-Rubaie, and a retired general, Nasser al-Amri. The Sunnis have shortlisted some generals from Saddam’s military and the current army.

Mr al-Maliki’s greatest challenge is to show that he can put an end to the worsening violence, in which 33 people were killed in attacks on Saturday and at least 24 yesterday.

William Patey, the British Ambassador, said that Mr al-Maliki was the right man, but experts gave a grim analysis of the situation. “There is not a lot of ground for optimism,” Joost Hiltermann, of the Brussels-based Crisis Group think-tank, said. “Fundamental questions remain unresolved.”

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