It was never completely stamped out, experts say, and Sunni and Shiite insurgents have used anti-U.S. sentiment and discontent with the Iraqi Interim Government (IIG) to attract adherents and provoke unrest. Their goal, says Kenneth Katzman, senior Middle East analyst at the Congressional Research Service, is to show that the IIC is "ineffective and illegitimate" because it can't guarantee security.

A Sunni insurgency continues in central Iraq. A Shiite rebellion led by cleric Muqtada al-Sadr has reignited in parts of Baghdad and the southern city of Najaf, holy to Shiites as the site of the Imam Ali shrine. The two movements are not coordinated, but experts say their cumulative effect is threatening the IIG led by Prime Minister Ayad Allawi.

Some experts say yes. The Brookings Institution's "Iraq Index," an ongoing compilation of data on Iraqi reconstruction, estimates that the number of insurgents has grown from roughly 5,000 to some 20,000 over the last several months. U.S. officials say it's impossible to get accurate figures. "These folks certainly don't sign up and register," says Harold Heilsnis, director for public inquiry and analysis in the Public Affairs division of the Defense Department. Michael O'Hanlon, senior fellow in security studies at Brookings and a co-author of the "Iraq Index," says a large number of former "fence-sitters" have recently joined the fighting. "They're young men who have no jobs, no investment in the new Iraq, and they're fed up," he says. "There's much more negativity and cynicism on the streets."

The Sunni insurgency has been centered in the so-called Sunni triangle region north and west of Baghdad. The Shiite rebellion led by Sadr is most visible in Najaf and Sadr City--a vast Baghdad slum of some 2 million--but has also spread to other cities, including Kut, Kufa, Basra, and Nasiriya. "The Sunni areas have been on fire for months," Katzman says. "Ramadi, Falluja, Baquba, and Samarra are effectively ungovernable--they're enclaves where insurgents can operate with impunity." Experts say insurgents are using those cities, particularly Falluja, as staging grounds for their operations and training centers for their fighters.

Until recently, most of the north and south were relatively calm. Then, on August 5, insurgents attacked three Mosul neighborhoods and fought Iraqi police, killing 12 people and wounding dozens in the fiercest fighting in the northern city since the occupation began. On August 9, a British soldier was killed in Basra, and Iraqi oil officials announced a one-day halt to oil exports from the southern city because of security fears.

Sadr's forces launched an uprising in Najaf and Karbala April 4 after U.S. forces closed Al Hawza, Sadr's newspaper, detained one of his top aides, and announced that Sadr was wanted for the murder of a rival cleric. Fierce clashes between Sadr's militia, the Mehdi Army, and U.S. forces lasted until Sadr declared a cease-fire on June 16. The agreement between Sadr and Iraq's interim government called for Sadr's followers to lay down their arms while their leader formed a political party; the hope was that he would enter the national political system and stand for election in next January's parliamentary elections.

Some experts are deeply skeptical. Jeffrey White, a Middle East security expert at The Washington Institute for Near East Policy, says the Mehdi Army was never disarmed or fully dismantled. Sadr, White says, "never moved fully into the political mainstream. I question whether he ever had any intention of doing that, or he just sought time to refit his troops."

On August 2, U.S. forces clashed with militia members outside Sadr's Najaf home; at the same time, Iraqi police were in the process of arresting a group of high-profile Sadr supporters. There were reports that U.S. forces had cordoned off the area and encircled Sadr's house. A U.S. military spokesman denied that, saying Marines new to the area had gotten lost in the neighborhood, come under attack, and retaliated. But Sadr and his followers saw these moves as preludes to his arrest. "Sadr felt he had an agreement with Allawi to be left alone," Katzman says. When troops came to his house, Katzman says, he considered the agreement broken and gave the go-ahead to his troops.

On August 5, Sadr supporters attacked a Najaf police station, setting off more than a week of intense clashes between Mehdi Army fighters and U.S. forces. Sadr's supporters used the city's revered sites, primarily the Imam Ali shrine and its adjacent ancient cemetery, to launch their attacks. Some 3,000 U.S. troops and hundreds of Iraqi security forces were deployed to Najaf to try to crush the uprising. Al-Sadr was reportedly lightly wounded by shrapnel August 13. Fighting stopped the same day to allow talks between the Mehdi Army and the IIG. Those talks broke down August 14, and the clashes resumed. U.S. military spokesmen said eight U.S. soldiers and at least 360 of Sadr's militiamen were killed in the violence. Sadr's aides dispute the second figure, saying far fewer of their fighters have died.

Popular support. "There's no doubt that [Sadr's fighters] are trying to cause damage to holy places [in Najaf] so the common people will turn against the interim government," says Lawrence J. Korb, senior fellow at the Center for American Progress. "The one card he's really had to play is his opposition to the occupation and the interim government," White says.

On August 9, he vowed to fight U.S.-led forces in Najaf "until the last drop of my blood has been spilled." He has urged his forces to fight on even if he is killed. Experts say the bravado is part of a deliberate strategy. "If he dies, he'll join his father and brothers [who were murdered by Saddam Hussein] and become a martyr," says Ahmed Hashim, a Middle East expert at the U.S. Naval War College. "If he's captured, the outrage will be great. And if there's a negotiated settlement, it'll be like [the uprising in] April, when his political standing grew tremendously. He wins in every case."

Hashim says Sadr has a solid base of 3 million to 5 million supporters, mostly Shiite, "the poorest of the poor in Iraq." Sadr is now trying to reach out to the broader Shiite community, with limited success. "We still don't see the Shia as a whole rallying around him," White says. "Sadr is fighting for a day in the political sun. [But] the mainstream Shia community doesn't support him." Many experts say Sadr doesn't have the stature--or command the respect--of a more experienced figure like Shiite Ayatollah Ali al-Sistani. "Sadr is an impetuous, power-hungry, angry young man," O'Hanlon says.

He's trying to. Hashim says Sadr gave a July 30 sermon denouncing the IIG as a puppet government, condemning the occupation, and saying the United States and Israel are trying to destroy Islam. "Those are all nationalistic messages that appeal to Sunnis too," Hashim says. "Sadr is trying to portray himself as a national leader." Experts say it's unclear if Sadr's message is winning over sizable numbers of Sunnis.

Experts say it is increasing its fighting capacity, improving its organization, and becoming more efficient. "The Sunni insurgency for the long term is more dangerous [than Sadr's movement]," White says. "It's more deeply embedded in the Sunni community, and it looks like it's developing some political manifestations." O'Hanlon says, "It's classic guerilla warfare. Phase I is hit and run, Phase II is frequent attacks aimed at undermining the government, and Phase III is an all-out war for power. They're firmly in Phase II right now."

"The Iraqi security forces are somewhere between helpless and inept," Katzman says. "Some units are doing better than before, but overall they're not anywhere near what's needed to deal with the insurgency." White disagrees. "We haven't seen the collapse we saw in April," he says, when many Iraqi forces ran away or refused to fight insurgents. Iraqi security forces have performed much better in the recent fighting, some experts say, battling insurgents in Mosul and Kut and holding their ground while under attack in Najaf. After being called in, U.S. forces took "operational control" of Najaf's police and national guard units to handle the crisis.

U.S. Central Command remains effectively in charge of the country's security, experts say. "[General George] Casey [commander of the multinational force] and [General John] Abizaid [commander of U.S. central command] are the architects of any security operations," Katzman says. However, since the June 28 handover of sovereignty, U.S. forces have worked closely with the Iraqi Interim Government, and U.S. commanders seek the approval of Iraqi leaders before undertaking sensitive missions. In Najaf, for example, U.S. officials said they would not send troops into the cemetery or the Imam Ali shrine without Allawi's approval.

Allawi has been tough on insurgents, saying repeatedly since taking office June 28 that there is no room in Iraq for armed militias. On August 7, he tried diplomacy, traveling to Najaf to seek a negotiated solution to the crisis. That attempt failed. On August 8, Allawi resumed his harsh rhetoric, denouncing rebel groups and vowing to crush militias that refuse to disarm. He also reinstituted the death penalty for a variety of offenses, including threatening national security. Experts see Sadr's revived insurgency as Allawi's first big challenge as prime minister. "How he deals with Sadr will influence [the public] views of him," White says.

The violence prompted officials to shut down production in Iraq's southern oil fields, the country's largest, August 9 after the Mehdi Army threatened to attack refineries, pipelines, and oil fields. Production resumed August 10 despite fears that attacks on those fields--which account for 1.8 million barrels a day, or 90 percent of Iraq's oil exports--could cripple the country's oil industry and boost already soaring world oil prices. Crude oil traded at a high of $46.58 per barrel in New York August 13.

Delegates to a national conference in Baghdad convened to choose an interim government assembly dispatched a delegation to Najaf on August 16 to negotiate with Sadr. Some experts say that, no matter how the Najaf crisis is resolved, conditions in Iraq will remain precarious. "The best we can hope for with the insurgency is that it can be pushed down to tolerable levels," White says. "It will be a long-term, violent resistance. It may get worse or better, but it won't be eradicated entirely."