BEIRUT -- An eruption of violence in Iraq is threatening to undo much of what American troops appeared to have accomplished before they withdrew, putting the country's stability on the line and raising the specter of a new civil war in a region already buckling under the strain of the conflict in Syria.
In the western Iraqi province of Anbar, Sunnis are in open revolt against the Shiite-dominated government of Prime Minister Nouri al-Maliki. Militants affiliated with al-Qaida have taken advantage of the turmoil to raise their flag over areas from which they had been driven out by U.S. troops, including the powerfully symbolic town of Fallujah, where American forces fought their bloodiest battle since the Vietnam War.
The Iraqi army, trained and equipped at great expense by the U.S. military before it pulled out in 2011, is struggling to hold its own against what is at once a populist revolt and a militant insurgency.
On Monday, Mr. Maliki urged the people of Fallujah to expel al-Qaida-affiliated militants to avert a full-on attack, echoing calls made by U.S. forces a decade ago when they warned residents to leave the town or suffer the consequences.
"The prime minister appeals to the tribes and people of Fallujah to expel the terrorists from the city in order to spare themselves the risk of armed clashes," Mr. Maliki said in a statement read on state television as convoys of troops, tanks and heavy equipment headed toward the town to reinforce troops who were surrounding it.
Instead, however, most residents were trying to leave, packing their possessions into cars and fleeing in any direction they could, just as they did ahead of the U.S. assault on the town in November 2004.
The Obama administration has responded to the crisis by promising to accelerate deliveries of extra weapons to the Iraqi government, including Hellfire missiles and surveillance drones. White House spokesman Jay Carney said U.S. officials are working with the Iraqi government "to develop a holistic strategy to isolate the al-Qaida-affiliated groups."
And a senior Iranian commander said Monday that Iran was ready to send military equipment to Iraq.
Gen. Mohammad Hejazi, the deputy commander of Iran's armed forces, told local journalists in Tehran that Iran was ready to support the Iraqi government in fighting the "terrorists" but was not planning to send troops.
"Such a request has not been officially made," Gen. Hejazi said, according to the government-controlled Islamic Republic News Agency. "Equipment and advice will be given if they ask for it, but as for forces, the Iraqis are very powerful themselves."
Most analysts and Iraqis say the problem is rooted, above all, in the Maliki administration's failure to reach out to Sunnis and include them in the decision-making processes of the coalition government, thereby enhancing a sense of Sunni alienation from the authorities in Baghdad that began when U.S. troops invaded and toppled Saddam Hussein, a Sunni, in 2003.
"Extra weapons and drones are not going to solve this problem. In fact, they will make it worse, because it will encourage Maliki to believe there is a military solution to this problem, and that is what perpetuates civil wars," said Kenneth Pollack of the Brookings Institution in Washington.
The latest violence erupted after Mr. Maliki dispatched troops to disperse a 1-year-old protest site in Anbar's capital, Ramadi, where Sunnis had gathered to air grievances against the government.
The upheaval that followed has evolved into a complicated three-way conflict in which almost all Sunnis have turned against the central government, though some have aligned themselves with militants from the al-Qaida-linked Islamic State of Iraq and Syria and others have not.
The New York Times contributed.