Three years after his U.S.-backed militia helped drive the Sunni insurgent group al-Qaeda in Iraq into hiding in Anbar province, Raad Sabah al-Alwani and other Sunni tribal leaders met here last week to fret over a new fear: the reemergence of Shiite cleric Moqtada al-Sadr’s militia.

Sadr, who recently returned from nearly four years of self-imposed exile in Iran, paraded his Mahdi Army through Baghdad’s Sadr City last week to press his demand that U.S. military forces leave Iraq. The cleric billed the march as a moment of national unity, saying all Iraqis were welcome, and the participants were not armed.

But for Alwani, the self-described military leader of the anti-insurgent “Awakening” movement, images of tens of thousands of Shiite militiamen parading through the capital marked a threat to efforts to move beyond the sectarian strife that once nearly plunged Iraq into civil war.

The day after Sadr’s march, Alwani said, he sat with other sheiks, local government officials and “high-ranking police and army officers” from Anbar’s capital, Ramadi, to discuss whether Sunnis across Iraq should soon form or revive their own, Sunni-dominated militias.

“They believe there will be no one to protect them, no one to force the evil away,” said Alwani, who hopes U.S. forces remain in the country past their scheduled Dec. 31 departure date. “That is why they feel a need to form a popular army — just to protect themselves.”

On Friday, Sadr’s spokesman announced that the cleric had left Iraq two days earlier and returned to Iran. But it was not immediately clear how long Sadr planned to remain there.

In Ramadi, and across Sunni-dominated areas, unease over Sadr’s march has come to symbolize growing frustration with Prime Minister Nouri al-Maliki, concerns about security and the political process, and fear of what many Sunnis see as Iran’s growing influence in Iraq’s affairs.

Maliki, a Shiite battling to hold his coalition government together, has been quoted as saying that the Mahdi Army, like any group, has the right to express itself in the new, democratic Iraq. Many Sadrist politicians also describe Sunni concerns as an overreaction, saying that their movement — including the Mahdi Army — has modernized and moderated as it became integrated into the political process.

But among Iraq’s Sunni minority, the fears of Sadr’s militia and Iran run deep.

“Al-Mahdi’s Army duty is very well known: It’s to kill the Sunni people and to evacuate Baghdad of the Sunnis,” said Ahmed al-Alwani, a Sunni lawmaker. “It is a shameful attitude by the officials to bless the march.”

Sunni leaders, who say they suspect Iran helped organize and fund the Mahdi Army’s march, warn that Sadr’s power play is becoming a recruiting tool for Sunni-dominated militias or terrorist groups.

Several of those groups helped fuel the insurgency against American forces in the months after the 2003 U.S.-led invasion. Now, some of their fighters hope U.S. troops will stay to help protect Sunnis against the rise of Shiite extremists.

“We made a mistake when we poured scorn on the American forces until our ammunition ran out while they were still keeping their arms and ammunition,” said Oday Mohammed, 35, a former member of the armed wing of the Islamic Army in Iraq. “Now we are facing two choices: either we should reconstruct our armed factions or we should beg the Americans not to leave Iraq.”

Some Sunni tribal sheiks say they may hold a march in the coming days, perhaps in Ramadi, to counter Sadr’s message. Yet Sunni politicians warn that concerns extend beyond Sadr, underscoring the tensions threatening Maliki’s efforts to maintain a stable government.

Although Sunnis account for just 20 percent of Iraq’s population, they were close to power for the 24 years in which Saddam Hussein, a Sunni, oppressively ruled the Shiite majority.

After his fall, clashes between Sunni and Shiite groups from 2004 through 2008 killed thousands and left many people, especially in diverse Baghdad, fearful of their neighbors.

Few observers expect a return to that kind of bloodshed, and some of the political upheaval subsided after Iraq’s unity government was formed in December.

But frustrations remain. In the coalition government, Maliki serves as prime minister while the Iraqiya bloc, a secular but Sunni-backed coalition, is supposed to control such influential ministries as finance and defense. Jalal Talabani, a Kurd, serves as president.

After months of promises that an appointment was imminent, however, Maliki and parliament have yet to agree on a defense minister.

Many Sunni politicians also remain unnerved by the de-Baathification laws designed to rid the government of Hussein loyalists. And though Sunnis initially refused to participate in the forming of an army after Hussein’s demise, many now complain of its overwhelmingly Shiite composition.

“Our worry is there is no balance right now,” said Nahda al-Daini, a Sunni lawmaker from Diyala.

Aifan al-Issawi, head of the Anbar provincial council’s security and defense committee, said officials in Washington and Baghdad need to take heed of the tension or local residents may “reconsider or change their hostile position toward al-Qaeda and other terrorist organizations and non-terrorist armed groups.”

“The march — and having two armies in one state — means there is a big crack,” Issawi said. “We considered the march a sign of a divided state.”

Concerns about Sadr’s march are being echoed by U.S. officials. In an interview with Iraqi media organizations this week, U.S. Ambassador James F. Jeffrey called the forming of militias by “political forces” a “huge poison that destroys any democracy.”

“Iraqis, who faced death during their last elections, and everybody who supports the parliamentary system, must deeply think of what had happened last week,” said Jeffrey, according to news reports.

Special correspondents Asaad Majeed and Aziz Alwan in Baghdad and Othman al-Mukhtar in Fallujah contributed to this report.