BAGHDAD — The twin explosions Wednesday at one of Iraq's holiest Shiite Muslim shrines, heavily damaged in an attack last year, dealt a powerful blow to the U.S.-led security plan, seen as a last chance to stem sectarian bloodshed in Baghdad and surrounding areas.
Officials imposed curfews, Iraqis hunkered down in their homes, and a top U.S. commander said he had a "sinking feeling" Wednesday after bombs leveled two minarets at the Golden Mosque in Samarra, 60 miles north of Baghdad.
Despite calls for calm from religious and political leaders, reports of revenge attacks against Sunni Muslim mosques began trickling in within hours of the 9 a.m. blasts, which came nearly 16 months after militants blew up the Shiite shrine's famed golden dome. The February 2006 blast, viewed as a turning point in the Iraq war, touched off a wave of reprisal killings and warfare that left an estimated 34,000 people dead and many more displaced.
The prospect of a replay of that violence caused panic in Baghdad, where residents stocked up on food and other supplies, driving up the black-market price for gasoline. Huge traffic jams formed as residents tried to hurry home.
"It is like a country about to be hit by a hurricane," said one Baghdad resident, who gave his name only as Tariq.
No one took responsibility for the attack, although U.S. officials suggested it bore the hallmark of Sunni insurgents linked to Al Qaeda. In a TV interview, Army Gen. David H. Petraeus, the top U.S. commander in Iraq, said he had a "terrible sinking feeling" when he heard the mosque had been hit again. But, he told ABC News, there was reason to hope that the Al Qaeda terrorist network had overplayed its hand.
"Frankly, it is our hope that this can galvanize the Iraqi leaders to unite against this form of extremism," he said.
Other observers took a more grim view.
"This attack may well prove to be the nail in the coffin of the security plan," said Joost Hiltermann, Middle East director of the International Crisis Group. "Now I think it is time for Plan B."
The attack threatened to deepen the crisis besetting Prime Minister Nouri Maliki's Shiite-led government, which has been unable to negotiate the political compromises that U.S. officials believe are needed to win the confidence of the disaffected Sunni Arab minority that feels sidelined after the ouster of Saddam Hussein.
Within hours of the blasts, followers of radical Shiite cleric Muqtada Sadr suspended participation in parliament to protest the government's failure to protect holy sites. Sadr's Al Mahdi militiamen have been blamed for many of the revenge attacks after last year's bombing at the shrine.
Maliki, who toured the ruins Wednesday, also faced a potential backlash from Shiite radicals who have remained on the sidelines during the security plan that has sent thousands of U.S. troops into the capital and adjacent regions.
As curfews fell on four volatile cities and reinforcements moved into Samarra, political and religious leaders on both sides of the sectarian divide lined up before TV cameras to appeal for restraint.
U.S. military planners had warned that Sunni Arab insurgents linked to Al Qaeda were planning spectacular strikes to provoke Shiites back into battle. One senior Pentagon official specifically named the Samarra mosque in March when outlining U.S. concerns.
"My guess is they are going to try a repeat of Samarra," the official said at the time, speaking on condition of anonymity because he was discussing internal planning. "They may go back to Samarra and say, 'We didn't really level the place.' Imagine that, perception-wise -- to go back to Samarra and finish the job."
The latest attack did almost that. Only the clock tower and walls were left standing. No casualties were reported.
Police at the scene said they heard two nearly simultaneous blasts coming from inside the shrine at 9 a.m., the U.S. military said in a statement.
The blasts kicked up a huge cloud of dust and sent food tumbling from the shelves at Hatam Khalaf's grocery store, about 200 yards from the shrine.
"I went outside to see what happened, and then I saw that the two minarets were gone. I was stunned," he said in a telephone interview.
President Bush denounced the attack and said he had dispatched troops to Samarra to help restore order.
"This barbarous act was clearly aimed at inflaming sectarian tensions among the peoples of Iraq and defeating their aspirations for a secure, democratic, and prosperous country," Bush said in a statement.
Earlier in Washington, White House Press Secretary Tony Snow sought to deflect blame from the U.S. military, noting that the guarding of Muslim shrines has mostly been handed over to the Baghdad government.
"You got to keep in mind, there's a lot of sensitivity about Americans being on Shia holy sites," Snow said at his daily briefing in Washington. "The Iraqis, for understandable reasons, have said, you know, we want to be able to protect our sites."