BAGHDAD (AP) — Iraq on Saturday was investigating an attack on a Sunni mosque in a volatile province outside Baghdad that killed more than 60 people and raised sectarian tensions during a fraught political transition.

Parliament speaker Salim al-Jabouri, a Sunni, told a press conference that a committee of security officials and lawmakers would announce its findings in two days. He did not say who might have been behind the attack, saying only that such violence was "carried out by the same hands (of those) who want to derail the process of building the government."

It remained unclear whether the attack in the village of Imam Wais on Friday was carried out by Shiite militiamen or insurgents of the Islamic State group, who have been advancing into mixed Sunni-Shiite areas in the Diyala province and have been known to kill fellow Sunni Muslims who refuse to submit to their harsh interpretation of Islamic law.

Local security officials said the attack began with a suicide bombing near the mosque entrance, followed by a raid by gunmen who stormed the building, opening fire on worshippers. At least 64 people were killed, including four Shiite militiamen who stumbled upon bombs planted by the militants as they rushed to the scene with security forces.

Sunni lawmakers offered a different account, saying Shiite militiamen had launched a reprisal attack on the mosque after their convoy was bombed.

The attack led two major Sunni parliamentary blocs to pull out of talks on forming a new government. The move creates a major hurdle for Shiite prime minister-designate Haider al-Abadi as he struggles to reach out to Sunnis to form a government by Sept. 10 that can confront the Islamic State extremists.

Jabouri heads one of the blocs that suspended talks, but he declined to comment on the move at the press conference, saying he was there in his capacity as parliament speaker.

Imam Wais village is located about 75 miles (120 kilometers) northeast of Baghdad in the ethnically and communally mixed Diyala province, which saw heavy fighting at the height of Iraq's sectarian conflict in 2006 and 2007.

Firat al-Tamimi, a Diyala lawmaker, said there are conflicting accounts surrounding Friday's events. He confirmed, however, that there was a bombing near the mosque prior to the assault on worshippers.

Iraqi President Fouad Massoum, a Kurd, condemned Friday's attack and appealed "to all for self-restraint and to act wisely." He promised the incident would be "properly investigated and its perpetrators held to account."

U.N. Secretary-General Ban Ki-moon said he's "deeply concerned about the impact such acts of sectarian violence will have on the already grave security situation and on the political process." The European Union said the "heinous crime" should not stand in the way of government formation and urged Iraqis to unite against violence.

Since early this year, Iraq has faced an onslaught by the Islamic State group and allied Sunni militants. The crisis has worsened in June, when the group seized Iraq's second-largest city of Mosul and subsequently declared an Islamic state, or caliphate, in territory under its control in both Iraq and neighboring Syria.

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Associated Press writers Vivian Salama in Baghdad and Maamoun Youssef in Cairo contributed to this report.