BAGHDAD, Iraq -- A leading Sunni politician on Saturday reaffirmed his party's commitment to being part of a coalition government and thanked insurgent groups for refraining from attacks during this week's parliamentary elections.

Adnan al-Dulaimi, a former Islamic studies professor who heads a Sunni Arab bloc expected to have a voice in the new National Assembly, said a power-sharing government was important to "safeguard the rights of Iraqis."

Earlier he predicted that Shiite religious parties will be unable to form a government -- even though they are widely expected to take the largest number of seats. That would open the door to a coalition of Sunnis, secular Shiites and Kurds, al-Dulaimi said in an interview Friday.

Two senior U.S. officials also called for a broad-based government and asked Iraqis to be patient as the ballots are counted. Results were expected within two weeks from election day Thursday.

"All reports indicate that Iraqis from all communities and regions turned out in large numbers with only limited reports of violence and irregularities," U.S. ambassador Zalmay Khalilzad and top U.S. commander Gen. George W. Casey Jr. said in a joint statement.

"This is a signal that the people of Iraq have chosen to become active participants in their country's future."

President Bush was to make a nationwide address on Sunday about Iraq. On Friday the White House called the elections historic. "We now are entering a critical period for our mission in Iraq," spokesman Scott McClellan said.

U.S. officials see al-Dulaimi, who leads the Iraqi Accordance Front, as a possible intermediary who could persuade some Sunni-led insurgent groups in restive Anbar province to join the political process.

Al-Dulaimi thanked insurgent groups for keeping to a pledge not to carry out attacks during Thursday's elections. Sunnis Arabs had boycotted the Jan. 30 elections, many heeding a warning by such groups not to vote.

"The resistance groups committed themselves not to attack but to protect voting centers and not allow any other group to attack them. They kept their promise and we thank them for this," he told a news conference.

In an Internet statement Friday, the Islamic Army in Iraq, a major insurgent group, said it was responsible for the absence of widespread election violence because it wanted to avoid harming Sunni Arab voters.

The statement, which could not be immediately verified, added that the jihadist group did not believe in democracy, only God.

Al-Dulaimi's prediction that the Shiites would be unable to form a government is by no means a certainty. Shiites account for about 60 percent of the country's 27 million people, and turnout in the Shiite heartland of southern and central Iraq was reported high.

Under the newly ratified constitution, the party with the biggest number of seats gets first crack at trying to form a government than can win parliament's endorsement. That is likely to be the coalition of Shiite religious parties that dominate the outgoing government.

Still, a government with strong Sunni Arab representation could help defuse the Sunni-dominated insurgency and allow the United States and its coalition partners to begin removing troops next year.

On Friday, Casey told Pentagon reporters in a video teleconference that he will make recommendations in the next few weeks about troop withdrawals from Iraq.

But he sought to dampen expectation that a successful election alone would end the insurgency and predicted insurgents may escalate their attacks to demonstrate they "are still strong and a factor to be reckoned with."

"We should not expect the insurgency to just go away because of yesterday's great success," Casey said. "But we should expect it to be gradually weakened and reduced as more and more Iraqis adopt the political process and the root causes of the insurgency are addressed by the new Iraqi government and by the coalition."

Before Thursday's election, Shiite religious politicians said they expected to win up to 120 seats -- down 26 from their current level. The Shiites and Kurds won a disproportionate number of seats in the January ballot because so many Sunnis boycotted the election. This time, Sunnis turned out in large numbers.

Jawad al-Maliki, a prominent Shiite legislator, said there was "no doubt that initial results show that we will be the strong bloc" but that a coalition would probably be required -- possibly with some Sunnis.

Another Shiite politician, Mouwafak al-Rubaie, said the Shiites would try to form an "inclusive" government even if they don't have to. He accused "some foreign embassies" of "working very hard" to manipulate the results.