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The Sunni tribesmen camped out on the edge of this one-time Iraqi insurgent stronghold are digging in and growing more organized, vowing to keep up their protests against a Shiite-led government they feel has left them behind.

Now a prominent Sunni sheik who once helped Americans battle al-Qaida is warning that protesters will seek to bring down the government if their demands aren't met. He speaks ominously that armed militants who once fought U.S. troops could rally to the cause.

"When we give up hope that the government can reform itself, we will call for toppling it," Sheik Ahmed Abu Risha said in his well-guarded family compound near the banks of the Euphrates. "If this government does not disband itself, we will head to Baghdad and stage protests in the streets and paralyze the government's work until it falls apart."

When the last U.S. troops withdrew from Iraq in December 2011, there was hope that majority Shiites and minority Sunnis and Kurds would learn to work together, resolve their differences and create a healthy democracy in a country with a history of strong-arm rule.

But as the 10th anniversary of the March 20, 2003 U.S.-led invasion approaches next month, the same sectarian tensions stirred up by the war are flaring again — in no small part, many Sunnis say, because of Prime Minister Nouri al-Maliki's attempts to consolidate power.

Nobody is predicting a return to open warfare. The Sunnis know they stand little chance of overpowering the Shiites, who dominate the government, army and police. Nor do the majority of Iraq's Sunni Arabs, including protesters, support al-Qaida and its frequent widespread bombings of Shiite targets.

But Abu Risha's comments in an interview on Monday with The Associated Press point to growing impatience among demonstrators in the vast western province of Anbar and other predominantly Sunni areas. Their bitterness has only increased since the shooting deaths of several demonstrators by Iraqi security forces in nearby Fallujah late last month.

Abu Risha carries considerable weight in Anbar. He took over leadership of the province's Sahwa movement, a Sunni tribal militia that joined the U.S.-led fight against insurgents, after his brother was assassinated in 2007. The Sahwa members' decision to fight alongside American forces is widely credited with helping turn the tide against al-Qaida.

Cars heading to the border with Jordan and Syria detour along a well-worn dirt path to avoid a tent city straddling the highway outside Ramadi that has become the focus for nearly two months of rallies. The more than 50 tents, festooned with tribal banners, now have cinder-block foundations built directly on the pavement to keep the rainwater out.

During a visit this week, power generators hummed as backhoes prepared for the next round of mass prayers and accompanying rally that are likely to draw tens of thousands again on Friday.

The arrest of bodyguards assigned to Finance Minister Rafia al-Issawi was the spark that set off the protests in late December. Al-Issawi hails from Anbar and is one of the power-sharing government's most senior Sunni politicians.

The demonstrations have little to do with the move against his staff anymore.

Sunni protesters complain they suffer from discrimination by the Shiite-dominated government. They accuse Baghdad of arbitrarily detaining members of their sect and say they are being targeted unfairly by a tough anti-terrorism law and policies designed to weed out members of Saddam Hussein's former regime.

Al-Maliki's government has called on security forces to show restraint toward the protesters and has set up a panel to consider their demands. It has taken some steps to address the grievances, like releasing detainees and moving to restore the pensions of some former state employees under Saddam.

Abu Risha said he and other senior protest figures are doing their best to keep the demonstrations peaceful. Protesters have occasionally thrown stones — including at a senior Sunni politician not long after the rallies erupted — but they appear to be heeding tribal and religious leaders' appeals not to take up arms for now.

"Horrible things would have happened if we hadn't been able to control these people," said Iraqi opposition lawmaker Ahmed al-Alwani.

That could change the longer protesters' rage simmers. Leaders of the demonstrations are demanding that the government hand over soldiers involved in the shooting deaths of five stone-throwing protesters late last month — the first such deaths since the protests began. Soldiers have since been killed in apparent retaliatory attacks.

Abu Risha told the AP that if another Fallujah-style shooting happens, armed militants will likely get involved.

"There were armed groups that wanted to attack the army, but we prevented them," he said. "If the army continues such acts, we will not stop the resistance groups from dealing with the army. ... The national resistance will take over the task of protecting the protesters."

Asked to specify which militant groups might take up arms, Abu Risha named the Islamic Army in Iraq and the 1920 Revolution Brigades.

The two Sunni insurgent groups targeted American forces after the 2003 U.S.-led invasion. They do not share al-Qaida's fundamentalist ideology and some in their ranks have actively clashed with the jihadist group.

Both have voiced support for the protests. So has al-Qaida's local franchise. That has prompted concern from Iraqi and U.S. officials, who fear that extremists could draw support from the demonstrators' feelings of alienation and hostility toward the Shiite-led government.

The prime minister's spokesman, Ali al-Moussawi, dismissed Abu Risha's comments as being "outside the framework of the law and the constitution." He said the influential clan leader does not represent all the protesters and is seeking personal gain from the demonstrations.

But regional experts at the Eurasia Group believe the government's handling of the Sunni opposition is fostering a longer-term security threat in Iraq's west. Analysts Crispin Hawes and Ayham Kamel wrote in a recent report that al-Maliki's approach "plays into the hands of Sunni extremists."

Michael Hanna, a Middle East expert at the Century Foundation, said Sunni political leaders have not done enough to stem political violence and terrorism. But he questioned whether Sunni militants would try to confront Iraqi troops head on.

"The leaders are probably pretty dubious of where that leads. The security forces, for all their shortfalls, have become a real fighting force," he said.

Some protesters say the Fallujah shooting marked a turning point that has galvanized their call for reform. An empty coffin commemorating the "martyrs of Fallujah" lies in the middle of the Ramadi protest grounds.

"The shooting shows that the government has become more repressive against the Sunnis," said Sunni cleric Fakhir al-Taie, who was one of at least 20 wounded during the Fallujah melee. "Now we view the government as an enemy to us. ... The core problem is that we have no confidence in this government."

Fear of further clashes with security forces is one reason that protesters have not yet tried to march on the capital. Organizers considered holding mass prayers in Baghdad last week but later decided against it. The government sealed off approaches to the capital just in case.

Baghdad has been spared large-scale protests so far. Several hundred worshippers rally in the courtyard of a prominent mosque after prayers each Friday but do not take their protests any further.

Demonstrators have taken to the streets in other cities with large Sunni communities, including Samarra, Tikrit and Mosul.

Abdul-Hameed Younis Hamouda, a 60-year-old tribal leader and one of the organizers in Mosul, acknowledges that the government has addressed some of the protesters' grievances, but says it still has a long way to go.

"The delay in meeting our demands is not in the government's interest," he said. "Our patience is running out."

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Associated Press writers Sameer N. Yacoub and Sinan Salaheddin in Baghdad contributed reporting.

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