A floundering government campaign to crack down on militias and increasing sectarian killings have many Shiites turning to militias for protection, particularly radical cleric Moqtada al-Sadr's violent Mahdi Army.
The US and British military have stepped up raids on its leadership after growing impatient with the new government's failure to arrest the militia's commanders.
But Sunday, two suicide car bombs in the capital and one in the troubled northern oil city of Kirkuk killed a total of 60 Iraqis, as new Prime Minister Nouri al-Maliki jetted off to Britain and the US for talks with Prime Minister Tony Blair and President George Bush on Iraq's crumbling security situation.
Such violence only strengthens the hand of the militias.
The two suicide car-bombsin Baghdad killed at least 42 people in the teeming Sadr City neighborhood, a Mahdi Army stronghold. The attacks followed a joint US and Iraqi raid overnight on a Sadr office in the area that ended with 15 Sadr supporters dead and two hostages freed, the US said in a statement.
Some residents blamed the US raid for the market attack, charging that it forced Mahdi Army members to abandon some of their impromptu checkpoints in the area that are meant to keep out attackers.
"When the Americans come through and break up the checkpoints, that's when we get hit by suicide bombs, like today," says Ahmed Awadh, a Sadr City resident who works in the Ministry of Trade.
"I support the Mahdi Army because they know us here, and we know them. Their checkpoints protect us," he says. "They know all the families, and who has business here. It's clear the Americans don't want to provide us with security. They've had three years.''
Immediately following the market blast, Mahdi Army militiamen poured out of the neighborhood's warren of alleys, shutting down dozens of streets and setting up checkpoints, trying to protect against follow-up attacks.
The district of about 2 million – 8 percent of Iraq's population – is largely policed by the militia. The group runs health clinics and religious courts, and arranges lodging for Shiite refugees from Sunni-dominated parts of the country.
Sadr's movement has built a powerful following because of its aid efforts, and Sadr is positioning himself as a voice for poor Shiites who have seen little tangible benefit from regime change. That follows the same strategy of his father, for whom Sadr City is named, who garnered enormous support among poor Shiites for speaking out against Saddam Hussein until he was killed by the regime in 1999.
"The police and Army don't protect us. When the Americans were here yesterday, they were shooting at our people here, not the criminals,'' says Mohammed al-Askhar, a Mahdi Army member who insisted on using only his nom-de-guerre, which means "Mohammed the Blondie."
Iraqi Prime Minister Nouri al-Maliki's "government has shown it's powerless. The residents of Sadr City will protect themselves. Everyone here is behind us. We will only disarm when the violence is over," he says.
Sadr and Mahdi Army members brush off allegations from US officials and Sunni Arab politicians that its members run some of the death squads that target Sunni Arabs in revenge attacks, like the organized murders of more than 30 in Baghdad's western Jihad neighborhood earlier this month.
There, gangs of gunmen roamed the streets for two hours, pulling Sunnis from their cars and homes.
Even on days without such high-profile killings, bodies of bound Sunni Arab victims, usually shot in the head but sometimes garroted with wire, are frequently found in empty lots along Sadr City's northern and eastern edges.
Thousands of Shiites have also been killed in sectarian attacks. In addition to Sunday's suicide bombings, seven Shiite construction workers were killed near the US Military's Camp Victory on Saturday.
Nevertheless, one US general says that he considers Sadr's militia, with its thousands of poorly trained irregulars and its growing reputation for sectarian killings, to be one of the country's gravest security threats.
"They're organized and they're spreading,'' he says.
After Prime Minister Malikitook his oath of office, he promised to restore security and outlined a detailed plan to suppress militias on both sides. US officials said they believed Maliki had the authority and respect to get the job done as a leader of the powerful Shiite Dawa Party, according to one senior US official.
But Mr. Sadr is a powerful member of the ruling coalition in his own right. His movement holds 30 seats in parliament, and his loyalists control four ministries. While once considered disorganized rabble rousers, the Mahdi Army has evolved into a social force to be reckoned with.
"Today, the Sadrists play a central part in government and parliament,'' the International Crisis Group, a Brussels-based think tank, wrote in a report earlier this month. "The Sadrist movement has deep roots, and its demands reflect many justified grievances."
Sadr's rise to power has some small parallels to the strength of the Shiite group Hizbullah in Lebanon. There, Hizbullah is seen by its supporters, mainly poor Shiites, as a protector and a provider of social services that a weak central government can't offer them.
As in Lebanon, where the government was hesitant to confront Hizbullah for fear of sparking civil war and had doubts about their own army's cohesion in such a battle. Maliki appears uncertain of his military's willingness to target Sadr's followers. Many Mahdi Army members also double as Iraqi soldiers and police. There could also be political fallout for Maliki if he appears to be an American puppet. .
Sadr has made the comparison himself with Hizbullah. Speaking on Friday, he vowed to support to the group.
"As the idol of America fell, so will the idol of Israel,'' he said.