The US military once regarded the Mahdi Army and its fiery black-turbaned leader as the greatest threat to Iraq's stability as the nation continues to grapple with a bloody insurgency and sectarian warfare.

But US military commanders now say a Sadr truce has been instrumental in bringing about a significant decline in the level of violence, although US and Iraqi forces are continuing raids and arrests of his militiamen.

In 2004, Sadr's men twice challenged US forces with armed rebellions and although they took a beating, the nationalist cleric emerged as a figure to be reckoned with.

But last month, Sadr ordered his estimated 60,000-strong militia to prolong for six months a ceasefire originally introduced in August aimed at halting attacks on US forces and rival armed groups. Senior members of his movement said the truce, announced after allegations Sadr's gunmen were involved in bloody clashes in the shrine city of Karbala, aimed to rein in wayward factions operating beyond the cleric's writ.

"The attempt is to reorganise the militia but not to dismantle it. It is also an effort to root out the rogue elements," one aide said.

Sadr himself, known as a "sayyid" or descendant of the Prophet Mohammed, (PBUH) is believed to have the power to command war or peace in Iraq but has had a long absence from the public eye.

In the past year, a number of senior Mahdi leaders have allegedly broken away from the main group and the US military claims many are running their own independent groups and carrying out sectarian attacks against the Sunnis. Since Basra province was handed over to Iraqi control by British forces in mid-December, it has become the theatre of a bitter turf war between the Mahdi Army and its Shia foes.

These include the Badr organisation allied to the Supreme Iraqi Islamic Council (SIIC) of powerful politician Abdel Aziz Al Hakim, and the smaller Shia party, Fadhila.

The Mahdi Army, created after the 2003 US-led invasion, became the most active and feared armed Shia group, blamed by Washington for death-squad killings of thousands of Sunnis. It is named after Al Mahdi Al Montazar (the Awaited Mahdi), in reference to the revered 12th imam who disappeared in 907.

Initially underestimated by US authorities and Iraqi officials, the son of revered Grand Ayatollah Mohammed Sadiq Al Sadr also wields massive influence in the corridors of power. Since he returned to Iraq's turbulent political scene in May last year after disappearing from public view for seven months, Sadr has been working hard to bolster his nationalist credentials.

After throwing his weight behind Shia politician Nuri Al Maliki in 2006, ensuring he became prime minister, Sadr then ordered his six ministers to pull out of the cabinet last April.

And in September it pulled out of the ruling Shia dominated coalition, further upsetting Iraq's already fractured political landscape. However, it retains 32 MPs in the 275-seat parliament.

The cabinet walkout was in protest at the government's refusal to set a timetable for the withdrawal of US troops-something favoured by a majority of Iraqis and especially Sadr's supporters. -AFP