For Abu Maha is a leader of Hojatoleslam Moqtada al-Sadr’s al-Mahdi Army in western Baghdad, a deadly force with such power that no politician dares take it on.

The thousands-strong militia and a political power base of 32 seats in Parliament have made Hojatoleslam al-Sadr’s militant Shia movement the strongest in Iraq. The group is blamed for many death squad killings, but has such grassroots appeal that even the Shia premier cancelled plans to clear Sadr City, its Baghdad stronghold.

Accompanied by The Times, Abu Maha cruises past Iraqi soldiers as he plans an attack in Ghazaliyah, a mixed neighbourhood that has been a battleground for months. Ghazaliyah abuts Shula to the north, another enclave of the al-Mahdi Army, and Abu Maha is looking to extend his militia’s influence. He has been watching Sunnis who fled to the neighbourhood from another part of western Baghdad, convinced that they are in league with the Sunni al-Qaeda terrorists. He says that his men will target them — just business as usual for the militant who has no qualms about shedding blood in his mission to protect the Shia.

He shares some of his chilling exploits that have ended with the now familiar sight of a corpse dumped on the street. In July, when Sunni insurgents were firing mortars toward Shula, Abu Maha and a team of fighters received calls from an informer and chased down four suspects by the telephone exchange. They beat the men, forced them into their cars and drove back to Shula. There, Abu Maha says, he took out his 9mm pistol and shot one of the suspects in the head. His gang killed the other three.

His company generally detains people for several days before deciding whether to kill them. In one recent case, Abu Maha says his men abducted a guard from a Sunni mosque. They were convinced that he belonged to a Sunni death squad called the Omar Brigades, known for killing Shias, but after beating and questioning him in a building behind Hojatoleslam al-Sadr’s Shula office, they decided that he was innocent and released him.

Abu Maha, who used to be a gun seller, is just one of the many foot soldiers in the al-Mahdi Army’s intricate command structure. He reports back to a head officer in the Shula office. He, in turn, turn reports to the Sadr City office.

The al-Mahdi Army calls its Baghdad headquarters the operation room. The space can change, but the top commanders always convene in Sadr City to go over strategy and instructions from Hojatoleslam al-Sadr, says a high-ranking officer calling himself Abu Bakr.

Abu Bakr says that he and a superior officer called Abu Haidar take turns to make a weekly trip to Najaf to receive Hojatoleslam al-Sadr’s commands. “Orders go from Najaf to every region’s operation room.” Hojatoleslam al-Sadr has apparently been tightening his grip on the movement. According to Abu Bakr, he has just sent to Sadr City a list of names of members who should be sacked for abusing their power. “Sayed [al-Sadr] is very angry and wants them fired.”

Such moves have fed speculation that the cleric is trying to rein in his group’s daily attacks on Sunnis, apparently fearful that the Americans or the Iraqi Government might soon strike against him. A campaign against the militia would be complicated because its members continue to work in the police, and count supporters in the official Army.

The Americans believe that Hojatoleslam al-Sadr no longer has full control of his soldiers and one senior military intelligence official said that some militants had formed splinter groups with funding from third parties such as Iran. Such breakaway factions were more likely to be found outside Baghdad.

US intelligence believes that the militia in the capital boasts 15 special forces companies and at least eight intelligence companies. Basra and Amara in the south are places where the cleric has had difficulty guarding his authority, he said.

But military officials admitted that it may suit him to have some elements operating under the cover of being a rebel faction. “There are probably elements that are not rogue but are deniable,” the officer said.

Abu Bakr smiles and makes clear that even if his boss is firming up his command, the killing of Sunni “terrorists” will not end soon. The plump middle-aged militia leader, who frequently bursts into laugher, praises the al-Mahdi Army’s most notorious Baghdad fighter, Abu Derra, whom some call the Shia al-Zarqawi. The Americans have been chasing this militant since July and some Sadrist political leaders have publicly disowned him.

On a recent visit to Sadr City by The Times, Abu Bakr warmly greeted Abu Derra. “He is the al-Mahdi Army’s first member. He kills many terrorists and we like him.”

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