Hoping to help prevent Iraq's bloody sectarian violence from turning into civil war, President George W. Bush urged Iraqis to exercise restraint in a critical "moment of choosing." Secretary of State Condoleezza Rice called on political factions to renew efforts to form a unity government. Bush praised Iraq's political and religious leaders who have taken steps - apparently with some success - to halt the unrest that exploded after Wednesday's bombing of one of Shiite Islam's holiest shrines. "Iraq remains a serious situation," Bush said Friday in a speech to The American Legion. "But I'm optimistic, because the Iraqi people have spoken... They want their country to be a democracy." Still, Bush, Rice and others employed unusually negative language, underscoring the gravity of the situation. There are fears in Baghdad and Washington alike that Iraq could be on the brink of civil war nearly three years after the US invasion ousted Saddam Hussein's regime. Appeals from religious leaders and an extraordinary daytime curfew in Baghdad and three nearby areas Friday curbed the sectarian fury that killed more than 140 people across Iraq after the bombing of a sacred Shiite shrine. Prime Minister Ibrahim al-Jaafari reached out to both Sunnis and Shiites, promising to rebuild the Shiite Askariya shrine in Samarra, whose famed golden dome was reduced to rubble in Wednesday's bombing, as well as Sunni mosques damaged in two days of deadly reprisal attacks. Al-Jaafari, a member of a Shiite religious party, also appointed a committee to determine who was responsible for the "Samarra catastrophe and what followed." The daytime curfew kept most vehicles and pedestrians off the streets of the capital Friday, preventing many people from reaching mosques for the main Muslim prayer service of the week but also curbing protests and preventing suicide attacks on places of worship. People were allowed to walk to neighborhood mosques, many of which were guarded by heavily armed Iraqi police and soldiers. Preachers at several leading Sunni and Shiite mosques urged their followers to maintain calm for the sake of the nation. But sectarian anger remained high, as did the threat of more violence. The Iraqi government announced another daytime curfew for Saturday in Baghdad and the surrounding provinces of Salaheddin, Babil and Diyala. The US military said it would operate additional security patrols for another 48 hours. "I do think that there's a concern that the sectarian tensions that outsiders are stoking in Iraq, that those same outsiders might try to stoke sectarian tension in other parts of the region," said US Secretary of State Condoleezza Rice. She named al-Qaida and terror leader Abu Musab al-Zarqawi as possible suspects, but said it is not clear who was responsible for "trying to stoke civil war in Iraq" and derail political consensus. "It's rarely been Iraqis who talked about civil war," she said. Although Friday was the calmest day since the Askariya bombing, two rockets were fired late Friday in a village southeast of Baghdad that includes a tomb revered by Shiites. There was no damage to the tomb, US and Iraqi officials said. The target was unclear. Two more rockets exploded in the British Embassy compound in Baghdad's heavily fortified Green Zone, causing minor injuries to two British workers, the US military reported. No further details were provided. Police found at least 27 bodies Friday in Baghdad and other cities and towns. Many were believed victims of sectarian violence, including five Shiite men killed by gunmen who burst into their home in Latifiyah south of Baghdad, according to police. In Samarra, a roadside bomb killed two policemen. A man and his wife in a passing vehicle were injured when police opened fire after the attack, police said. An explosion set fire to an oil pipeline south of the city, police said. The Shiite-Sunni confrontation threatens to scuttle US hopes for a government of national unity among Shiite, Sunni and Kurdish parties that won seats in the December 15 parliament election. The US hopes such a government can win the trust of the disaffected Sunni Arab community, the backbone of the insurgency, and calm the violence so American and other international troops can begin heading home. But the biggest Sunni political bloc in parliament withdrew from talks with the Shiites on a new government to protest attacks on Sunni mosques. US officials remain hopeful the Sunnis will return to the bargaining table, but the crisis may delay forming the government, which had been expected by mid-May. US Ambassador Zalmay Khalilzad acknowledged the grave danger facing Iraq but said the shrine bombing also presented the country with a "moment of opportunity." "I think this attack has had a major impact here, getting everyone's attention that Iraq is in danger ... that they must lead and compromise with each other to bring the people of Iraq together and to save this country," he told reporters during a conference call. In an overture to the Sunnis, the country's top Shiite political leader, Abdul-Aziz al-Hakim, issued a statement expressing regret over the deaths of all Iraqis. He said those who carried out the Samarra attack "do not represent the Sunnis in Iraq," blaming instead Saddam Hussein loyalists and religious extremists from al-Qaida in Iraq, led by Abu Mussan al-Zarqawi. "This is what al-Zarqawi is working for, that is, to ignite sectarian strife in the country," al-Hakim said in the statement broadcast by Iraqi television stations. "We call for self-restraint and not to be dragged down by the plots of the enemy of Iraq." A Sunni spokesman, Dhafer al-Ani, called al-Hakim's statement "a step on the road of healing the wounds." But he said his Iraqi Accordance Front was still waiting for an apology for failing to protect Sunni mosques from reprisal attacks. Meanwhile, supporters of radical Shiite cleric Muqtada al-Sadr met Friday with representatives of a Sunni clerical organization, the Association of Muslim Scholars, to discuss a "charter of honor" prohibiting killings among Iraqis. Al-Sadr's militiamen were responsible for at least some of the attacks on Sunni mosques, although the cleric joined other Shiite clerics in calling for calm. Both al-Sadr and the Association strongly oppose the US presence in Iraq. In his statement Friday, the prime minister announced a series of security measures to curb the unrest, including a ban on vehicles entering or leaving Baghdad, more patrols in flashpoint neighborhoods, and a ban on carrying unauthorized weapons in the streets. The vehicle ban in Baghdad was aimed at preventing people from leaving the capital for Samarra, 95 kilometers (60 miles) to the north and was not expected to be applied vigorously elsewhere, government officials said on condition of anonymity because they are not authorized to speak for the prime minister.