At least two sets of negotiations aimed at stemming the anti-coalition attacks are under way. In the Shiite south, members of the U.S.-appointed Iraqi Governing Council (IGC) and influential religious figures have met with rebel Shiite cleric Muqtada al-Sadr) So far, Sadr has agreed to withdraw his forces from government buildings and police stations in Najaf, but U.S. forces remain poised to capture or kill him. In Falluja, a center of Sunni resistance, sporadic fighting broke a fragile cease-fire as negotiations to persuade local leaders to hand over anti-coalition insurgents continued. "I think we have to be prepared and prepare ourselves that there may be further military action in Falluja," said General Richard B. Myers, chairman of the Joint Chiefs of Staff, on April 15.

In Najaf, negotiators include members of the Supreme Council for Revolution in Iraq (SCIRI) and the Da'wa Party. Both are moderate Shiite religious parties that favor an Islamic state in Iraq, and both have representatives on the IGC. Religious leaders negotiating with Sadr include the son of Grand Ayatollah Ali al-Sistani, Iraq's

most powerful Shiite cleric, and Grand Ayatollah Mohammed Said al-Hakim, another top cleric based in Najaf. Iranian officials were reportedly invited by Britain to participate in the talks; however, the extent of their involvement in the talks remains unclear.

In Falluja, negotiations are being led by Sunni IGC members, according to press reports. Among them: Moshen Abdul Hamid, a religious scholar and the head of the Iraqi Islamic Party (IIP). The IIP favors the peaceful establishment of an Islamic state. Another negotiator is Ghazi Ajil Al-Yawar, a leader of the powerful Shammar tribe, which has thousands of members north of Baghdad between the Tigris and Euphrates rivers. U.S. civilian and military officials met directly with city representatives April 16, according to press reports.

Violence has flared on two fronts. A largely Sunni force is fighting coalition troops in Falluja and north of Baghdad, and Shiite fighters clashed with them in Baghdad, Najaf, and other southern cities. Hundreds of Iraqis were reported killed in Falluja, a predominately Sunni city of some 250,000 encircled by U.S. forces. Dozens of additional Iraqi casualties were reported in Baghdad and southern cities as a result of fighting between coalition and Sadrist forces. U.S. military officials said April 15 that some 92 U.S. troops and more than 700 insurgents have been killed since April 1.

They appear to include members of the former ruling Baath Party, other Sunnis opposed to the occupation, and foreign jihadists. Their main base is in the so-called Sunni triangle north of Baghdad, though they are also believed to have staged attacks in the capital, as well as in Kurdish and Shiite areas. It is unclear if the Sunni insurgents are several autonomous groups or a centrally directed force.

It is made up of Shiite fighters associated with the Imam al-Mahdi Army, an illegal militia headed by Sadr. U.S. military officials say the militia consists of between 1,000 and 6,000 fighters; Sadr's spokesmen claim to have 10,000 armed rebels. News reports indicate that sympathy sparked by the rebellion may have spurred additional Shiites to join the fight.

U.S. military officials have suspended military operations in the cities of Falluja, Karbala, and Najaf, but they are gathering forces around these cities in case truce talks break down. They are also continuing to pursue and kill anti-U.S. fighters in other areas. They have indicated that they will agree to a negotiated end to the violence on both fronts if the insurgents meet certain demands. "There is not a purely U.S. military solution to any of the particular problems that we're facing here in Iraq today," Army General John P. Abizaid, the commander of U.S. Central Command, said April 12. "It's a combination of military and political action, both on the Iraqi and the American side, and on the coalition side, that will ultimately work towards a more secure environment here." Earlier comments from the military struck a harsher note. On April 6, for example, Brigadier General Mark Kimmitt, the chief military spokesman in Iraq, said coalition forces would "attack to destroy the Mahdi Army."

In Falluja, coalition authorities are reportedly demanding the capture of men responsible for the brutal killing and mutilation of four American contractors March 31, as well as of insurgents involved in attacks on coalition forces. In Baghdad and southern Iraq, Sadr must withdraw his forces from cities they hold, dissolve his militia, pay for damaged and looted property, and surrender to authorities. In exchange, U.S. officials said Sadr may turn himself in to Iraqi political leaders instead of U.S. troops. "Clearly, it is the intent of the governing council to bring Sadr to justice. How they go about doing that I think will probably end up being a uniquely Iraqi solution," Abizaid said.

It has harshly criticized the recent U.S. military moves. On April 10, it issued a statement calling for an end to the "collective punishment" of the people of Falluja. Adnan Pachachi, the council's first president after its establishment in July 2003, called the Falluja siege "unacceptable and illegal." One council member, a Shiite sheik named Abdul Karim al-Muhammadawi, suspended his membership to protest the coalition's attacks. IGC members said they were not consulted before the coalition began counterinsurgency operations against Falluja and Sadr. Had they been, they added, they would have opposed them.

No. But to help secure the country, U.S. generals have asked for two more combat brigades--some 10,000 to 15,000 additional soldiers--to strengthen their forces as the June 30 transition to Iraqi political control approaches. U.S. officials maintain that the situation has not gotten out of hand and say that most of the country is now stable. Still, the upheaval has been the most violent since the end of major combat operations in May 2003. Previously, anti-coalition violence had been largely confined to Sunni areas.

Experts warn that the occupation would be undermined if moderate Shiites join Sadr's movement or the insurgency develops into a national movement that unites Sunnis and Shiites. Much depends on how the occupying forces respond to the insurgency, experts say. "Sadr is trying to turn his battle with the United States into a Shiite issue, not a law-and-order issue. He's making the argument that all Shiites are under attack," says Phebe Marr, author of "A History of Iraq." President Bush has vowed the violence will not disrupt the planned handover of power to Iraqis on June 30.

It's unclear. There are two levels of support: those who fight and provide direct assistance to the fighters and those who sympathize with them. U.S. officials say they do not believe they are facing a broad-based Sunni resistance.

U.S. officials say former Baathists draw support from stores of cash and weapons left behind from the days of Saddam Hussein. Foreign jihadists may be getting support from al Qaeda and terrorism-financing networks. U.S. intelligence has indicated that some tribal leaders are now supporting the insurgents, according to The New York Times. It is difficult to know how much of the general Sunni population is actively involved in supporting the insurgency.

News reports indicate that sympathy is significant, fed by anti-U.S. anger among many Sunnis. The heightened fighting in recent days has led some Sunni clerics to sanction open warfare against the U.S.-led occupation, further strengthening the resistance, according to press reports. Rebels appear able to move freely and hide among the population of Falluja and other Sunni areas. This is a classic problem in counterinsurgency warfare, because an insurgency can succeed "even if only 4 or 5 percent of the population is actually participating, if the rest of the population sits on the sidelines," says William Flavin, a professor of multinational stability operations at the U.S. Army War College.

Some Sunni tribal and political leaders sit on the U.S.-backed IGC. There are also thousands of Sunnis who have joined the Iraqi security forces, served on U.S.-backed town councils, and participated in reconstruction efforts--sometimes at the cost of their lives. Some experts say they believe that a silent majority of Sunnis does not support the armed rebellion, but is waiting to see how things turn out and will not speak out against the resistance.

Sadr, 31, formed his Mahdi Army in August 2003. He appears to have used the past eight months to stockpile arms and prepare for the possibility of an armed rebellion, some experts say. His support is organized via a network of mosques and charities spread throughout much of Shiite-dominated southern Iraq. Experts say this network is largely inherited from his father, a former top Iraqi Shiite cleric who was killed in 1999. Sadr has opposed the U.S.-led occupation since its start. However, he did not call for armed resistance until April 4, after U.S. forces closed his organization's newspaper, arrested one of his close associates, and announced Sadr was wanted for the April 2003 murder of a U.S.-backed cleric, Ayatollah Abdul Majid al-Khoei.

Juan Cole, a professor of history at the University of Michigan, estimates that some 20 percent of Shiites--or about 3 million Iraqis--are sympathetic to his cause. The coalition's recent moves against Sadr may have attracted more fighters and won him additional sympathy. "Many Shia believe the United States provoked him," says Kenneth Katzman, a Middle East analyst at the Congressional Research Service. Sadr is also thought to receive some financial support from Iran.

Experts say Sadr's network of supporters is far smaller than that of 73-year-old Sistani, the country's pre-eminent Shiite figure. For his part, Sistani has dismissed Sadr as a cleric of minor significance and has called on both the U.S.-led coalition and Sadr to seek a political resolution to their dispute. Other Shiite militias and political organizations appear to be staying out of the fighting. Among them: the 10,000 Iran-trained fighters associated with SCIRI and the Da'wa Party's militia.

At least nine cities have reported violent clashes since April 4:

• Baghdad: Dozens of Shiites have been killed in Sadr City, a vast Shiite slum of 2 million that is a stronghold of Sadr support. At least 8 U.S. soldiers died in the fighting there. While the coalition regained general control of the area by April 12, U.S. forces continued to "destroy and capture enemy targets and secure government facilities and police stations," Kimmitt said.
• Najaf: Sadr remained holed up April 16 in this city of 500,000 that is sacred to Shiites. While his militia ceded control of police stations and government buildings according to the terms of an April 12 agreement, he retained his hold on the Shrine of Ali, the holy tomb of the Prophet Mohammed's son-in-law and the fourth caliph. Some 2,500 U.S. forces encircled the city, poised to attack if talks collapsed.
• Kut: U.S. troops retook the city from Sadr's forces April 9. On April 7, Ukranian coalition troops under Polish command in central Iraq had withdrawn under fire from Sadr supporters.
• Kufa: Sadr's forces reportedly continued to maintain a few checkpoints in the center of this city April 16, despite Sadr's pledge to hand the city back over to Iraqi security forces. Kufa is Sadr's hometown and his stronghold; the mosque in which he gives his regular Friday sermons is there.
• Karbala: Sadr's forces reportedly continued to maintain a limited presence in parts of this holy city despite an agreement to withdraw, news reports said. U.S. officials said the situation was generally stable. Karbala is the site of the death of Ali's son Hussein in 680 A.D.
• Nasiriya: The city was calm by April 8. Heavy gun battles with Italian forces were reported April 6.
• Amara: The city was relatively calm by April 12, with just two reports of attacks on coalition forces, the U.S. military said. On April 6, British troops killed 15 Iraqis and wounded eight in fighting with Sadr's forces.
• Diwaniya: By April 12, the U.S. military said the situation was stable, with only sporadic mortar attacks against coalition forces. On April 7, news reports said there was significant fighting between Mahdi Army and Spanish forces.
• Basra: Sadr's forces seized control of the governor's office April 5, but stood down the next day after negotiations with British forces.

Conceivably, though so far experts say there is not much evidence of substantive military cooperation. For most of the 20th century, Iraqi Sunnis dominated their Shiite countrymen and women, who make up some 60 percent of the population. Still, some news reports indicate that both Sunni and Shiite fighters attempted to join the battle in Falluja, and some recent attacks in Baghdad are reported to be Sunni-Shiite operations. On a non-military level, anti-U.S. sentiments have driven Sunnis and Shiites closer. They have organized food and medicine shipments to Falluja and, the Associated Press reported, held joint prayer services in the southern city of Basra. These developments, some commentators say, hold the potential for a broader-based national resistance movement.