An offensive by insurgents that threatens to dismember Iraq seemed to slow on Saturday after days of lightning advances as government forces regained some territory in counter-attacks, easing pressure on the Shia-led government in Baghdad.
As Iraqi officials spoke of wresting back the initiative against Sunni militants, the Islamic militant group that seized much of northern Iraq has posted photos that appear to show its fighters shooting dead dozens of captured Iraqi soldiers.
Meanwhile, neighboring Shia Iran held out the prospect of working with the U.S. to help restore security in Iraq.
U.S. President Barack Obama said Friday that he was reviewing military options, short of sending troops, to combat the insurgency. The United States ordered an aircraft carrier moved into the Gulf on Saturday, readying it in case Washington decides to pursue a military option after insurgents overran areas in the north and advanced on Baghdad.
Ships like the USS George H.W. Bush, which are equipped with sophisticated anti-ship and anti-aircraft missiles, are often used to launch airstrikes, conduct surveillance flights, do search, rescue, humanitarian and evacuation missions, and conduct seaborne security operations, a U.S. defense official said.
In a visit to the city of Samarra, Prime Minister Nouri al-Maliki vowed to rout the insurgents, whose onslaught has put the future of Iraq as a unitary state in question and raised the specter of sectarian conflict.
The gains by the Islamic State of Iraq and the Levant (ISIL) have alarmed Maliki's supporters in Iran and the United States, which helped bring him to power after invading the country and toppling former Sunni dictator Saddam Hussein in 2003.
But having encountered little resistance in majority Sunni areas, the militants have now come up against the army, which clawed back some towns and territory around Samarra on Saturday with the help of militia.
"We have regained the initiative and will not stop at liberating Mosul from ISIL terrorists, but all other parts," said Major-General Qassim al-Moussawi, spokesman for the Iraqi military's commander-in-chief, pointing out areas the army had retaken on a map with a laser pen.
In Salahuddin province, pictures on a militant website appear to show masked fighters of the ISIL loading the captives onto flatbed trucks before forcing them to lie face-down in a shallow ditch with their arms tied behind their backs. The final images appear to show the bodies of the captives soaked in blood after being shot.
Iraq's top military spokesman, Lt. Gen. Qassim al-Moussawi, confirmed the photos' authenticity on Sunday and said he was aware of cases of mass murder of captured Iraqi soldiers in areas held by ISIL.
Militants in control of Tikrit, about 30 miles north of Samarra, planted landmines and roadside bombs at the city's entrances, apparently anticipating a counter-attack by government forces. Residents said the militants deployed across the city and moved anti-aircraft guns and heavy artillery into position. Families began to flee north in the direction of Kirkuk, an oil-rich city that Kurdish forces occupied on Thursday after the Iraqi army fled.
Security sources said Iraqi troops attacked an ISIL formation in the town of al-Mutasim, 14 miles southeast of Samarra, driving militants into the surrounding desert on Saturday.
The army also reasserted control over the small town of Ishaqi, southeast of Samarra, to secure a road that links the city to Baghdad and the cities of Tikrit and Mosul farther north.
Troops backed by the Shia Asaib Ahl al-Haq militia helped retake the town of Muqdadiya northeast of Baghdad, and ISIL was dislodged from Dhuluiya after three hours of fighting with tribesmen, local police and residents, a tribal leader said.
Masked fighters under the black flag of ISIL aim to revive a caliphate that would span a fragmenting Iraq and Syria, redrawing borders set by European colonial powers a century ago.
Maliki traveled on Friday to Samarra, one of the cities targeted — although not seized — by ISIL fighters who now prevail in a string of Sunni cities and towns running south from Mosul.
"Samarra will not be the last line of defense, but a gathering point and launchpad," he told military officers after Iraq's most influential Shia cleric urged people to take up arms and defend the country against the insurgents.
"Within the coming hours, all the volunteers will arrive to support the security forces in their war against the gangs of ISIL. This is the beginning of the end of them," Maliki said in comments broadcast on Iraqi television.