U.S. officials have been repeatedly stunned and frequently thwarted in the past three years by the extraordinary power of Muslim clerics over Iraqi society. But in the sectarian violence of the past few days, that power has taken a new and ominous turn, as rival hard-line Shiite clerical factions have pushed each other toward ever more militant and anti-American stances, Iraqi and Western officials say.
Even Grand Ayatollah Ali al-Sistani, the paramount Shiite cleric to whom the Americans have often looked for moderation, appears to have been outflanked by younger and more aggressive figures. After a bomb exploded in Samarra at one of Iraq's most sacred Shiite shrines on Wednesday, many young Shiites ignored al-Sistani's pleas for calm, instead heeding more extreme calls and attacking Sunni mosques and killing Sunni civilians, even imams, in a crisis that has threatened to provoke open civil war.
On Saturday, the sectarian bloodletting continued in Karbala and the Baghdad area, bringing the death toll since the bombing to more than 200.
As the critical moment of Friday Prayer approached, U.S. officials and their allies were left almost helpless, hoping that Iraq's imams would step up to calm the crisis. But that hope gave way to the realization that the clerics could do as much harm as good, and for the first time since the toppling of Saddam Hussein, the Iraqi authorities imposed an unusual daytime curfew to keep people from attending the sermons.
A Western diplomat in Baghdad, speaking on condition of anonymity, said that sectarian divisions and sectarian violence are not new, but the difference is that Shiites, showing their patience is limited, reacted violently.
The violence and heightened militancy has come in part from a competition among Shiite factions to present themselves as the protectors of the Shiite masses. The main struggle has been between the leading factions, both backed by Iran, and their spiritual leaders.
Many of the retaliatory attacks after the bombing were led by Mahdi Army militiamen loyal to Muqtada al-Sadr, the Shiite cleric whose anti-American crusades have turned him into a rising political power. His rival Abdul Aziz al-Hakim, the cleric and leader of the Supreme Council for the Islamic Revolution in Iraq, defended the right of Shiites to respond to the bombing, and has shown a new willingness to publicly attack the U.S. role in Iraq - once the preserve of al-Sadr. Al-Hakim commands his own powerful militia, the Badr Organization.
The violence and escalating rhetoric among Sunnis and Shiites has left the mostly secular Iraqi leaders favored by the United States farther than ever from power.
"I think people are rapidly losing confidence in the political class, and I don't blame them," said Adnan Pachachi, a former foreign minister and a member of the shrinking secular alliance led by the former interim Prime Minister Ayad Allawi.
The fact that many hard-line political leaders are also clerics complicates the situation. The Iraqi leaders, for instance, can say one thing to U.S. officials while spreading a different message to a vast network of followers through mosques and militias. After al-Hakim on Wednesday accused the U.S. ambassador to Iraq of being partly responsible for the Samarra bombing, he distanced himself from the statement and met with the ambassador, Zalmay Khalilzad.
But on Friday, clerics loyal to al-Hakim's political party repeated the accusation against Khalilzad, and it quickly spread to the street, with some Shiites rallying in the southern city of Basra to demand Khalilzad's removal.
To some, the crisis of the past few days has underscored a longstanding U.S. failure to reach out effectively to moderate Islamists who might give them better access to the Iraqi masses. From the earliest days of the U.S. occupation in 2003, U.S. officials seemed to place most of their faith in secular figures like Allawi and Ahmad Chalabi, thinking they had popular support. At the same time, they also gave positions of authority to al-Hakim and other conservative religious figures, thinking they would play a lesser role in the new Iraq. But al-Hakim and others used their positions to help build their political base.
"The Americans knew what was coming, but they underestimated the power - they thought they could control the power of the clerics," said Hatem Mukhlis, a secular Sunni Arab politician who met with President Bush before the war.
Despite Iraq's relatively secular government over the past century, some Iraqis say, the country remains a part of the broader Islamic world, where the bonds between religion and the state are much deeper than most Americans seem to understand.
Iraqi Shiites in particular have rallied around their religious leadership in the past, most recently during the 1991 uprising against Saddam, but also on earlier occasions, including the 1920 revolt against the British.
"What's happened over the last three years is that there has been an ongoing crisis," said Laith Kubba, a former adviser to Prime Minister Ibrahim al-Jaafari who is now out of politics. "Even many Iraqis didn't accurately foresee the situation, that in an Iraq so highly polarized, religious leaders would become the rallying points."
Clerics have never been as influential among Sunnis in Iraq, who lack the religious hierarchy of the Shiites. Partly for that reason, the Sunnis were unable to organize as effectively as the Shiites, who dominated the January 2005 elections.
But the example of the Shiites, who formed a powerful political alliance under al-Sistani's guidance, pushed Sunnis toward their own religious leaders in the December vote.
To some extent, the U.S. government did recognize a need to court moderate religious figures who could play roles in Iraq's future. Even before the 2003 invasion, U.S. officials allied themselves with exiled clerics like Ayad Jamal Addin and Sheik Abdel Majid al-Khoei, a member of one of Iraq's most prominent Shiite families who was close to al-Sistani.
But the Americans seemed unaware of the complex and deadly rivalries among Iraq's religious factions. After being brought back to Iraq by the Americans in 2003, al-Khoei was stabbed to death in the Shiite holy city of Najaf by followers of al-Sadr. That killing led the U.S. occupation authority to issue an arrest warrant for al-Sadr, which was dropped after he led two bloody uprisings in 2004 and became one of Iraq's most powerful figures.