The campaign by the al-Qaida-inspired Islamic State militants has raised the specter of the sectarian warfare that nearly tore the country apart in 2006 and 2007, with the popular mobilization to fight the insurgents taking an increasingly sectarian slant, particularly after Iraq's top Shiite cleric made a call to arms on Friday.
The visit to Iraq this week by Gen. Ghasem Soleimani, leader of Iran's secretive Quds Force and its most powerful general , has confirmed longtime suspicions by the Sunnis that al-Maliki was too close to Iran, a mostly Shiite none-Arab nation that Sunni Arab states, including powerhouse Saudi Arabia, see as a threat to regional stability.
The Islamic State has vowed to march to Baghdad and the Shiite holy cities of Karbala and Najaf, home to some of the sect's most revered shrines, in the worst threat to Iraq's stability since U.S. troops left in late 2011. The militants also have tried to capture Samarra, a city north of Baghdad and home to another major Shiite shrine.
Iran has seen thousands volunteer to defend the shrines and its president, Hassan Rouhani, told a crowd at a stadium near the Iraq border: "We declare ... that the great Iranian nation will not miss any effort in protecting these sacred sites."
Al-Maliki insists that the call to arms by the Iranian-born Grand Ayatollah Ali al-Sistani was for all Iraqis and claimed, without producing evidence, that those who responded included Sunnis.
That did not stop a new cycle of sectarian violence, with the spark coming this week from the Islamic State's posting on the Internet of pictures purporting to show its fighters killing scores of captured Shiite soldiers.
That was followed by the slaughter by Shiite militiamen of nearly four dozen Sunni detainees in the city of Baqouba, northeast of Baghdad, late Monday, as well as the discovery Tuesday of the bullet-riddled bodies of four young Sunnis in a Shiite neighborhood of Baghdad and a bomb attack that killed 12 in an outdoor market in the capital's Shiite Sadr City district.
On Wednesday, a bomb blast killed four and wounded 11 in the mostly Sunni district of Ghazaliyah in western Baghdad.
Meanwhile, the government in India said 40 construction workers have been seized near Iraq's second-largest city, Mosul, which Sunni fighters captured last week.
The Turkish Foreign Ministry said its diplomats were also investigating a Turkish media report that militants grabbed 60 foreign construction workers, including some 15 Turks, near the northern Iraqi oil city of Kirkuk.
Ethnic Kurds now control Kirkuk, moving to fill a vacuum after the flight of Iraqi soldiers. They too are battling the Sunni extremist militants.
Iraqi Foreign Minister Hoshyar Zebari said Wednesday that his country had formally asked the U.S. to launch airstrikes against positions of the Islamic State.
Gen. Martin Dempsey, the chairman of the U.S. Joint Chiefs of Staff, confirmed the U.S. had received a request for air power to stop the militants, but highlighted the uncertain political situation in Iraq.
"The entire enterprise is at risk as long as this political situation is in flux," told a Senate panel Wednesday. He added that some Iraqi security forces had backed down when confronted by the militants because they had "simply lost faith" in the central government in Baghdad.
U.S. officials say Obama has shifted his focus away from airstrikes as an immediate option, in part because there are few clear targets the U.S. could hit, though that could change if intelligence agencies can identify clear targets on the ground.
Republicans continued to insist Wednesday that Obama bore the blame for allowing the insurgency to strengthen because of his decision to withdraw U.S. forces from Iraq in late 2011 after more than eight years of war. Washington and Baghdad failed to reach a security agreement that would have allowed American forces to stay longer.
"What's happening in Iraq is a direct result of the president's misguided decisions," said Rep. Duncan Hunter, R-Calif., a Marine reservist who served two combat tours in Iraq. "Militarily, the U.S. won in Iraq, but the hard-fought and hard-earned gains of our servicemen and women have been politically squandered by the president and his administration."
Associated Press writers Sameer N. Yacoub and Qassim Abdul-Zahra in Baghdad, AKaty Daigle in New Delhi, Julie Pace and Bradley Klapper in Washington, and Suzan Fraser in Ankara, Turkey, contributed to this report.