GENEVA (AP) — Reports of Islamic militants massacring scores of captured Iraqi soldiers are "deeply disturbing" and those responsible for it must be brought to justice, U.N. Secretary-General Ban Ki-moon said Monday.

The U.N. chief warned against sectarian rhetoric in Iraq that could inflame the conflict and carry grave implications for the entire region.

He said he welcomed the statement on the need for unity in Iraq made by Grand Ayatollah Sayed Ali Al-Sistani, who he said "represents a deeply influential voice of wisdom and reason."

The Islamic militants who overran cities and towns in Iraq last week have posted graphic photos on a militant website that appear to show masked fighters of the Islamic State of Iraq and the Levant, or 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 show the bodies of the captives soaked in blood after being shot at several locations.

Iraq's chief military spokesman, Lt. Gen. Qassim al-Moussawi, confirmed the photos' authenticity Sunday and said he was aware of cases of mass murder of captured Iraqi soldiers in areas held by ISIL.

"Reports of mass summary executions by ISIL are deeply disturbing and underscore the urgency of bringing the perpetrators of such crimes to justice," Ban said.

He also called on all Iraqi leaders across the spectrum of political, military, religious and community posts to ensure that their followers avoid acts of reprisal.

Ban urged the international community to unite in showing solidarity with Iraq as it confronts "this serious security challenge" and called for full respect for international humanitarian law and human rights law in efforts to counter terrorism and violence in Iraq.

U.N. human rights chief Navi Pillay warned Friday against "murder of all kinds" and other war crimes in Iraq, saying the number killed in recent days may run into the hundreds.