A daytime curfew was imposed in Baghdad and nearby provinces Friday, in a bid to stifle further sectarian violence in Iraq. State television said the government has also ordered people to be off the streets in Baghdad and the nearby provinces of Diyala, Babil and Salaheddin Saturday.

More than 200 people have already been killed in recent days in a wave of reprisals over Wednesday's bombing of a sacred Shi'ite Muslim shrine.  A new report says the sectarian violence has placed Iraq at a precarious crossroads.

In most areas, people stayed off the streets.  But in the Sadr city area of Baghdad, followers of the radical Shi'ite cleric Moqtada al-Sadr defied the curfew, and heeded his call to attend Friday prayers.  Al-Sadr called on his followers not to attack Sunni Muslims.

The bombing of the Askriya shrine in the town of Samarra Wednesday sparked a wave of sectarian violence.  Some religious leaders appealed for calm. But their calls went unheeded in some quarters, as angry Shi'ites, who consider the shrine sacred, engaged in reprisal attacks on Sunnis, whom many Shi'ites blame for the destruction of the shrine. 

U.S. officials said the attack makes the job of forming a new government tougher for Iraqis, but they remain upbeat.  In a speech Friday, President Bush said the elections in Iraq in December make him optimistic for the country's future.

"We can expect the coming days will be intense," said Mr. Bush.  "Iraq remains a serious situation.  But I'm optimistic, because the Iraqi people have spoken."

But a new report by the non-partisan International Crisis Group (ICG) is less optimistic.  The report, to be issued next week, says the Samarra attack is only the latest and bloodiest indication that Iraq is teetering on what it calls the threshold of wholesale disaster.  An advance copy was provided to VOA.

Speaking from Amman, Jordan, ICG Middle East Program Director Joost Hiltermann says Iraq is in danger of sliding into full-scale civil war.

"What happened in Samarra, and, of course, the fallout in terms of reprisal attacks against Sunni Arabs, is leading to a downward spiral of violence that, if it is not reversed, could lead to civil war," he said.

No one has claimed responsibility for the Samarra attack.  But Western officials say suspicion falls on al-Qaida in Iraq.  Mr. Hiltermann says no one knows who did the bombing, but adds that al-Qaida in Iraq has carried out anti-Shi'ite attacks in the past.

But, he says, Shi'ite officials in the fledgling Iraqi government have ordered their own attacks on Sunnis.

"But in the past year, we've seen that a couple of Shi'ite parties in government have taken advantage of their control over the security apparatus to mete out revenge, not against any specific perpetrator of anti-Shi'ite attacks, but against the Sunni Arab community more broadly," he added.

In what is expected to be its most controversial recommendation, the ICG calls on the international community to face the unpleasant prospect that Iraq will fall apart, and plan to contain any negative effects on regional stability and security. It says failure to anticipate such a possibility may lead to further disasters in the future.