After a weekend of sleepless nights, emergency meetings, and an unprecedented three-day curfew, Iraq has managed to stave off its worst fear after last week's destruction of a major Shiite shrine: That the country's small-scale civil conflict was about to bloom into a bloody and wide-ranging war between its sects.

But disturbing signs are emerging that Iraq's sectarian powder-keg is still highly volatile.

A pattern of politics drawn along sectarian or ethnic lines has strengthened in the wake of Saddam Hussein's rule. Leading moderate voices like Shiite Grand Ayatollah Ali al-Sistani have taken harder lines, and the growing authority of unelected clerics in determining Iraq's future is presenting new hurdles to the unity government most experts believe is needed to bring stability.

Two Shiite mosques were attacked Sunday and a bomb on a bus in the city of Hillah killed five people despite restrictions on movement that kept Baghdad streets deserted and businesses shuttered.

On Saturday night, representatives of militant Shiite cleric Moqtada al-Sadr and Sunni clerics from the powerful Muslim Scholars Association prayed together in a televised ceremony from Baghdad's Abu Hanifa mosque, a Sunni landmark. The clerics condemned recent attacks on Shiite and Sunni houses of worship and jointly forbade any actions leading to fitnah, or strife among Muslims.

Political leaders from all factions, who received a series of personal calls from President Bush on Saturday, echoed those sentiments in a separate meeting.

"Last night [at] the meeting between the different political parties, we agreed on some important points that might cool things down, like promises not to attack mosques,'' says Saleh al-Mutlak, a leader of the main Sunni front in parliament. "The general environment was not that bad, they are listening now, [the] Shiites know the civil war will hurt everybody including themselves."

"Everyone believes that the prospect for a civil war has diminished significantly in the course of the last several days, and that's clearly a good thing,'' US Ambassador Zalmay Khalilzad told reporters in a conference call on Saturday.

Shiite militias remain heavily armed and emotional, and on Sunday continued to move into some Sunni neighborhoods in the capital. Clerics are emerging as the only voices that can quell the violence, even as they've come under pressure from their followers to demand revenge. Even Ayatollah Sistani has advocated the founding of additional sectarian militias, drawn from southern tribes, to protect Shiite interests.

"It may well be that things will die down now,'' says Joost Hilterman, who runs the International Crisis Group's (ICG) Middle East Project in Amman, Jordan. "But the structural dynamic still points toward civil war, and the institutions that could restrain it have become severely weakened."

Sectarian violence since the Shiite Askariyah Shrine in Samarra was destroyed last Wednesday has claimed at least 250 lives, and the Sunni-based Iraqi Islamic Party says 120 Sunni mosques have been attacked. Dozens of the dead have been found executed, their hands bound, on the outskirts of Baghdad.

Though Ambassador Khalilzad and other American officials say the crisis has been averted for now, they have few resources to impose the kind of national unity government many believe is necessary for peace.

"I think that what the crisis has demonstrated in my view is that it has increased the need for the establishment of a unity government, it has made it more necessary,'' he said. "There are forces that are determined in seeking and trying to provoke a civil war ... and it is very important given that fact that there is a national unity government that Iraqis do not fall into that trap of sectarianism, sectarian conflict."

The US is also calling for the disarming of sectarian militias - as it has done without success for much of the past two years. But a unity government and an end to militias are precisely what seems least likely in the wake of recent events.

Iraq's dominant Shiite parties, led by the Supreme Council for the Islamic Revolution in Iraq and Dawa, as well as clerics like Ayatollah Sistani have long nurtured a vision of a unified Iraq dominated by its Shiite majority, replacing the Sunni-minority governments that have dominated Iraq throughout its history. Sunni Arabs, adrift in a country in which sectarian death squads have operated against them out of the Shiite-controlled interior ministry and hoping to regain their past position, are unlikely to stand down.

"All these things are necessary and none of them are likely,'' says Pat Lang, a former head of the Defense Intelligence Agency's Middle East bureau and a retired colonel with a counter insurgency background. Shiites and Sunnis "are contestants for the loot.... it's not about being Iraqis in an idealized Iraq but the real one. These are groups that are contesting power and they'll continue to do so."

Mr. Hiltermann's organization released a report on civil war in Iraq on Sunday, saying it could be averted if a national unity government is formed and militias disarmed. But Hiltermann says that while that may be the best way forward, he's skeptical that will happen.

"I don't see a solution, frankly. But if there is to be a solution it will have to come from the US expending a lot of political capital to convince them that the only way to keep Iraq united, which is a shared interest, is to form a government of national unity,'' he says. "The military and the police have been rebuilt in a sectarian fashion, even though that's not the intent, and so the security forces can end up playing a role in sectarian fighting rather than to dampen it, and that's been what has been going on."

A measure of how seriously the threat of all-out civil war is being taken can be found in the recommendations of Monday's ICG report.

"The international community, including neighboring states, should start planning for the contingency that Iraq will fall apart, so as to contain the inevitable fallout on regional stability and security."