BAGHDAD — Iraq's capital lurched closer to a renewed cycle of sectarian slaughter Tuesday after the bodies of a Sunni cleric and his aides, allegedly kidnapped by Shiite militiamen, were found in a Baghdad morgue and dozens of inmates were killed in a prison as insurgents battled security forces about 35 miles north.
The Muslim Scholars Association said Imam Nihad al-Jibouri and two of his aides were executed after being abducted by men dressed as security forces, killings reminiscent of the tit-for-tat violence of the worst days of Iraq's 2005-2007 civil war. The Sunni group warned of retaliation.
Baghdad has remained relatively calm amid a rampage in the north by al-Qaida-inspired militants from the Islamic State of Iraq and Syria. But with thousands of Shiite volunteers answering a call to arms from religious leaders and the Shiite-led government, many Sunnis in the capital and elsewhere fear reprisal attacks.
"There is a real risk of further sectarian violence on a massive scale," U.N. Secretary-General Ban Ki Moon warned Tuesday, as he urged Iraqi political and religious leaders to avoid incitement.
The United States was also pressuring Prime Minister Nouri al-Maliki, widely accused of failing to prevent the crisis, to bridge the sectarian divide. It has made clear that U.S. military support is contingent on the Maliki government undertaking political reforms.
Meanwhile, sectarian violence is on the rise. Jibouri and his assistants had been abducted in the religiously mixed neighborhood of Saidiyah four days before their bodies turned up in the morgue Monday, the Muslim Scholars Association said.
The group, a Sunni religious organization that the U.S. military long suspected of involvement in the insurgency against American troops, said in a statement that "these crimes won't go unpunished."
It added: "The day will come when we punish all the criminals and those who stand behind them."
Saidiyah was a flash point for sectarian killings during the civil war, when Sunni and Shiite death squads roamed the streets, filling morgues to the bursting point.
Also Tuesday, a car bomb in Baghdad's Shiite Sadr City district killed 12 people and wounded 30 in a crowded outdoor market, police and hospital officials said. No one claimed responsibility for the bombing, but attacks targeting Shiite districts are routinely the work of Sunni militants.
Reports of mass killings also have been emerging from the confused battlefields across the country as government forces attempt to recover from their humiliating rout a week ago, Shiite militias join the fray and ISIS militants continue to try to seize territory.
As insurgents continued to bear down on Baghdad from a number of northern locations Tuesday, the country's biggest oil refinery, in Baiji, was shut down. Turkey evacuated its consulate in the southern oil hub of Basra.
In Baqubah, capital of the religiously mixed Diyala province, 52 prisoners were killed as government troops battled to hold off an ISIS assault, Maj. Gen. Qassim Atta, a spokesman for Iraq's military, told the National Iraqi News Agency.
Other reports put the death toll at 44. There were conflicting reports on how the men died, with some saying the security forces killed the inmates. Twitter accounts affiliated with ISIS said the men were executed at the hands of the police.
The fighting in Baqubah represented the closest that ISIS and its allies have come to the capital.
With Iraq's Shiite neighbor rallying to support Maliki and the United States sending up to 275 troops to protect its embassy in Baghdad, the longtime adversaries have found themselves with mutual interests.
As the United States weighs its options for action, it has taken the unusual step of having its diplomats engage with their counterparts from Iran to discuss possible cooperation to help stop the march of ISIS. The White House has ruled out military cooperation with Tehran, however.
President Barack Obama is considering an array of options for combating the Islamic militants, but he is not expected to approve imminent airstrikes in Iraq, in part because there are few clear targets that could blunt a fast-moving Islamic insurgency, the Associated Press reported, citing U.S. officials.
Officials said Obama had made no final decisions and didn't rule out the possibility that airstrikes ultimately could be used, particularly if a strong target becomes available.
The White House has continued to emphasize that any military engagement remains contingent on the government in Baghdad enacting political reforms and ending sectarian tensions, which had been rising even before the incursion of ISIS last week, with thousands killed since late last year.
Republicans have criticized Obama's handling of Iraq, but Congress remains deeply divided over what steps the United States can take militarily.
The White House said Obama will discuss Iraq with congressional leaders today.
Information from the New York Times and Associated Press was used in this report.