RAMADI, Iraq -- As Rafe al-Essawi, the embattled Sunni leader, sped south on a desert highway last week to attend the funeral of a political ally who was assassinated, his cellphone rang with a warning: Up ahead, Iraqi soldiers, backed by two helicopters hovering overhead, planned to arrest him.
Mr. Essawi and his entourage turned around and raced back to Ramadi, meeting up with Sunni tribesmen who vowed to protect him.
"The sheiks said to me, we are ready to defend ourselves," Mr. Essawi said.
Mr. Essawi was until recently Iraq's finance minister and among the highest-ranking Sunni politicians. That he is now on the run from his own government in Anbar Province, alleging widespread persecution of Sunnis, is the latest sign that persistent sectarian tensions are undermining any lingering hopes of political stability and national unity.
As Iraq marks 10 years this week since the American invasion, Anbar Province -- the site of some of America's bloodiest battles and one of its greatest successes -- has emerged as the fulcrum of a rising Sunni resistance against Iraq's Shiite-controlled central government and the Syrian government of President Bashar al-Assad across the border.
With American influence severely diminished, the crosscurrents buffeting Anbar have aggravated the fault lines left when the United States withdrew.
"It's dangerous to have an unhappy minority population that borders Syria," said an American diplomat, speaking on the condition of anonymity, in accordance with protocol. "You have the potential for what's in Syria to come to these western provinces."
Mr. Essawi appears an unlikely figure to emerge as a focus of the conflict between Sunnis and Shiites. He is generally regarded as a voice of moderation in a country where a sense of Sunni embattlement under a Shiite-dominated government is widening. He is quick to point out that he played a pivotal role in cooperating with American forces to defeat Al Qaeda here, as a counterpoint to Prime Minister Nuri Kamal al-Maliki's tendency to equate the expression of Sunni grievances with terrorism.
"No one will accept Al Qaeda to return to Anbar," he said, in an interview from his hiding place in Ramadi. But he described the heart of Sunni anger like this: "They see Maliki as just a Shiite leader, not an Iraqi leader."
Indeed, a rising sense of Sunni disenfranchisement extends beyond the date palm groves and farmlands of Anbar, to the cities of Mosul and Samara that, like Ramadi, have been the site of weekly protests, and into neighborhoods of Baghdad.
The fear that Mr. Mailiki was out to sideline and punish the Sunni burst into the open even as American troops left at the end of 2011. At that time the government sought the arrest of the Sunni vice president, Tariq al-Hashemi, on charges of running a death squad. He has since fled to Turkey and been sentenced to death by an Iraqi court. Mr. Hashemi was never a favorite on the Sunni street, and his fate did not endure as rallying cry.
Other Sunni leaders are also in hiding, but it is Mr. Essawi's problems that appear a pivot point for the Sunnis. He sought refuge here in the compound of Sheik Ahmed Abu Risha, a tribal leader who led the Sunni Awakening, the movement in which former insurgents were paid by Americans to switch sides and fight against Al Qaeda in Iraq.
Abu Risha himself now faces an arrest warrant for financing terrorism, and considers himself one more Sunni target of Mr. Maliki's government, which since American forces left has used the country's terrorism laws against Sunni leaders in a campaign that American officials and analysts believe is politically motivated and based on flimsy evidence.
"We are the ones who defeated Al Qaeda," Abu Risha said. "We are the moderates against sectarianism."
And now, the men here say they are again picking up weapons, girding for a fight with the central government, and speaking the language of insurrection.
"We are in an emergency and we have fear and I'm defending the people," said Sheik Teheen al-Assawi. Mr. Assawi, a diminutive man in his early 70s, arrived at Abu Risha's compound Saturday morning wearing an ammunition vest. Slung over his shoulder was an assault rifle almost as tall as he was.
In a significant move, Mr. Maliki has responded to the call to arms among the sheiks of Anbar -- many who formerly worked hand in hand with the Americans at the height of the Awakening, when the Sunni insurgency was tamed -- with one of his own.
Another tribal leader, Sheik Hamid al-Hayes, has denounced the protest movement and joined with Mr. Maliki to form a new Sunni militia in Anbar to protect the interests of the central government. After several meetings with Mr. Maliki, Mr. Hayes said he had recruited 3,500 fighters that would provide intelligence to the local army and the police and protect neighborhoods.
"As for the sheiks that do not agree with this, they must reconsider what they say, as it will be very dangerous for the future," he said.
On a tabletop next to Abu Risha sat a wooden box containing a medal, encased in red velvet, awarded to him by the former American commanding general here, Gen. Ray Odierno, who himself wrote a letter to Mr. Maliki saying there was no basis to allegations that Mr. Essawi had links to terrorism. Abu Risha ticked off his losses from the war: Six brothers and his father were killed, and nearly 50 members of his extended family.
The 10th anniversary of the invasion, he said, "is a black day."
"The Americans, they don't make lasting friends," he said. "They eventually betray."
The Sunni protest movement around the country began in December after the government arrested several of Mr. Essawi's bodyguards at his home in the fortified Green Zone in Baghdad. The American ambassador, Robert Stephen Beecroft, happened to visit at the time of the raid and looked on helplessly as an event unfolded that he knew could have lasting repercussions. "He was very upset," Mr. Essawi said.
Mr. Essawi has vowed to stay in Iraq, and he denies he was trying to flee to Jordan -- as some officials believed -- when the security forces sought his arrest recently. "I've said many times that I would not leave Iraq, even if it's risky for me," he said.
But even Mr. Essawi, usually a voice of moderation, now seems to have adopted the language of militancy. He refers to the Iraqi army as a "militia," and speaks with the machismo this region is known for.
"This is Anbar," he said. "We defeated Al Qaeda. We will defend ourselves from the militias."
Tim Arango reported from Ramadi, Iraq, and Michael R. Gordon from Washington. Duraid Adnan and Yasir Ghazi contributed reporting from Ramadi.
This article originally appeared in The New York Times.