Iraq's prime minister blamed "outlaw criminals" on Saturday for alleged mass executions, following reports that dozens of civilians were killed by Shi'ite militias in Diyala province.
"It's not permitted for people to take the law into their own hands and punish others whenever they want to settle scores," Haider al-Abadi told a gathering of Sunni and Shi'ite religious and political leaders in Baghdad.
Abadi, a moderate Shi'ite Islamist who has sought reconciliation between Sunnis and Shi'ites, had called on Wednesday for an investigation into accusations that Shi'ite militias systematically executed at least 72 people in the village of Barwanah.
Accusations of such mass atrocities by Shi'ite militias threaten to undermine Abadi's efforts to win Sunni Muslim support to battle Islamic State, which grabbed large parts of northern and western Iraq last year.
The Shi'ite militias took the lead in battling the radical jihadist movement and keeping it from overrunning Baghdad after the Iraqi army nearly collapsed last summer.
Abadi said those responsible for the Barwanah killings were driving some Sunni Iraqis into the arms of Islamic State. "These are outlaw criminals implementing their own agendas to divide Iraqis," he said.
When Islamic State pushed into Sunni communities last year, it was welcomed by many Sunni Muslims who were alienated by the previous government of Shi'ite Islamist Nuri al-Maliki, under whom they said Sunnis were targeted with mass arrests.
Other political and religious leaders, including Iraq's most powerful Shi'ite cleric Grand Ayatollah Ali al-Sistani, have echoed Abadi's call for an investigation, and the United Nations has also supported a probe.
"The government must investigate the alleged attacks on civilians in the areas where operations took place," Sistani's aide Ahmed al-Safi said in a sermon at the Imam Hussein shrine in the Shi'ite holy city of Kerbala.
However, some were skeptical an investigation would be meaningful.
"What happened in Barwanah has happened in many areas and it will happen again. ISIS will do it, militias will do it," said independent Sunni Muslim lawmaker Mithal al-Alusi.
