Baghdad - The secular party of Ayad Allawi, a former interim prime minister once derided as an American puppet, won a wafer-thin victory in Iraq's election, setting the stage for a protracted period of political uncertainty and possible violence that could threaten plans to withdraw American troops.

The outcome, announced Friday, was immediately challenged by Prime Minister Nouri Kamal al-Maliki and his supporters in the State of Law coalition, who hurled accusations of fraud and made vague references to the prime minister's power as commander in chief.

Several parties have cried fraud as their fortunes waxed or waned in the slow vote count, an ominous reminder of an Iraqi political culture where winning is everything and compromise elusive. Western observers and an independent election commission have said they saw no signs of widespread fraud. Allawi galvanized the votes of millions of Sunnis - who boycotted the last parliamentary elections in 2005 - to build his edge of 91 to 89 seats over his nearest rival, al-Maliki. That falls far short of the majority of 163 of the 325 seats that he needs to form a government.

Iraqi political experts interviewed Friday doubted that Allawi would succeed in assembling a governing coalition. But even if he did, they said, it would take at least until July, possibly even longer, a potentially destabilizing stretch in which a disgruntled al-Maliki would serve as caretaker prime minister.

In a statement that seemed to reflect American concerns about the potential for violence, U.S. Ambassador Christopher R. Hill and Gen. Ray Odierno, the top American military commander in Iraq, praised "the overall integrity of the election" and called on political parties to "refrain from inflammatory rhetoric or action." There had been hope that the election would spell an end to Iraq's sectarian politics. And though the balloting shattered the sectarian political template that brought al-Maliki to power in 2005, when an alliance of Shiite parties dominated the election, the outcome re-emphasized the country's sectarian and regional divides and the deepening schism between Arabs and Kurds.

The vote in part reflected dissatisfaction with al-Maliki's ability to provide security, government services, and jobs. Allawi appealed to Iraqis tired of the past domination of Iraqi politics by religious parties; others responded to his image as the sort of strongman leader they have lacked since Saddam Hussein was ousted.

Reactions in Iraq ranged from jubilation to fear. Some people partied in the streets, honking horns and firing weapons in the air; others stockpiled food in case of violence and curfews.

"Nobody felt happy in Diyala," said Qais Jihad, 30, referring to the pair of bombs outside a cafe, killing 43 people who gathered to await results. "It is a win with a bloody flavor. Now we want to finish with election troubles ... so we can stop Iraqis' bleeding."

A jubilant Allawi said he would work with any group that was willing to join him in forming a government. "We will not exclude anyone," he said. "Our coalition is open to all."

Allawi's buoyant mood contrasted sharply with the atmosphere in the prime minister's camp on Friday evening, where al-Maliki angrily vowed to challenge the vote as fraudulent. "No way we will accept the results," al-Maliki said. "These are preliminary results."

Last week, al-Maliki released a statement saying the election commission needed to respond to demands for a recount in order to prevent a "return to violence." The statement pointedly noted that al-Maliki remained the country's commander in chief of the armed forces.

On Friday, however, he stressed that his opposition would be "through legal channels to transfer the authority in a peaceful and transparent manner."

The Independent High Electoral Commission, which oversees elections, said the vote had been free of widespread fraud and that it will not conduct a recount. Commission members said the panel had investigated hundreds of allegations of fraud, but had found none that would significantly change Friday's results.

Ad Melkert, the top U.N. representative in Iraq, called the vote "credible," and added, "We have not found evidence of systematic failure or fraud of widespread nature."

Al-Maliki's State of Law coalition and other political groups now have three days in which to lodge new complaints, which will be investigated by the election commission. The results will then be sent to Iraq's Supreme Court.

Because of his two-seat advantage in the new parliament, Allawi will most likely get 30 days in which to form a broader coalition to reach the required 163-seat majority. He has already been in talks with members of the Kurdish Alliance.

Friday's results showed that a fractured Iraqi electorate had split the country's 18 provinces among four different political groups.

Al-Maliki won Baghdad, the most populous province, and six predominately Shiite provinces south of the capital, while Allawi won or ran virtually even in five provinces in the north and west of the country with large Sunni populations.

The Iraq National Alliance won a single province and the Kurdish Alliance won three Kurdish provinces in the north.

Among the areas in which Allawi ran surprisingly strongly was Kirkuk, a province in northern Iraq, which sits atop billions of barrels of oil. It is contested by Kurds, who want to integrate it into the semiautonomous Kurdistan region, and Arabs, who want to keep it part of Iraq.

Allawi's coalition and the Kurdish Alliance each picked up six seats in the province. The balloting in Kirkuk - and accusations of fraud there and in Ninevah and Diyala provinces, also in Iraq's restive north - could lead to an escalation of violence in those places, Iraqi and American officials said.

Some observers believe Allawi, who is a secular Shiite, will have great difficulty cobbling together the necessary support and that al-Maliki might be able to return as prime minister.

"His problem is that while he is a pragmatist who could make a deal with the Kurds and some Shiite factions, one of his main constituencies are Sunni Arab nationalists who would not countenance an alliance with the Kurds, unless the Kurds made impossible concessions on Kirkuk and other disputed areas," said Joost Hilterman of the International Crisis Group. One result, he said, could be that the main Shiite parties could regroup and form a government similar to this one.

If Allawi failed to form a government, that task would fall to al-Maliki, who would be likely to seek an accommodation with the Iraqi National Alliance of al-Sadr.