The deepening crisis in Iraq with over one million fleeing their homes and the rising number of civilian deaths has provoked grave concern within the United Nations, Al Jazeera reported.
In a statement released on Monday UN Secretary General Ban Ki Moon said he was "deeply troubled by persistent reports of violations of human rights and international humanitarian law taking place in Iraq."
Violations have included summary executions of captured soldiers and detainees, indiscriminate shelling of civilian areas, and the abduction and murder of members of ethnic and religious communities.
The fighters have allegedly posted more than a dozen videos showing beheadings and shootings of combat soldiers and police officers, as well as apparent targeting of people based on their religion or ethnicity, including Shia and minority groups such as Turcomans, Shabak, Christians, and Yezidis.
In a recently released report, the UN Assistance Mission in the country and the UN Human Rights Office (OHCHR) cited alleged abuses by both the Iraqi Security Forces and the armed group Islamic State of Iraq and the Levant (ISIL).
The statement comes as the group Sunni armed group, ISIL, now named the Islamic State, announced the establishment of a "caliphate" straddling Syria and Iraq, urging other groups to pledge allegiance.
In an audio recording released on Sunday, the group formerly known as the Islamic State of Iraq and the Levant declared its chief, Abu Bakr al-Baghdadi, "the caliph" and "leader for Muslims everywhere".
An official document was also released, in English and several other languages describing Baghdadi as "the sheikh, the fighter, the scholar who practices what he preaches, the worshipper, the leader, the warrior, the reviver, descendant from the family of the Prophet, the slave of God".
The document urged Muslims to "gather around your caliph, so that you may return as you once were for ages, kings of the earth and knights of war."
Al Jazeera's Imran Khan, reporting from Baghdad, said that a caliphate was effectively an Islamic republic led by one leader, regardless of national boundaries.
He added however that Sunni groups which have fought with the Islamic State group in Iraq have yet to pledge allegiance.
With continued violence at least 1,300 people were killed in Iraq, and another 1,250 injured since 5 June in fighting in Nineveh, Salah al-Din and Diyala alone, according to UNAMI and OHCHR. At least 900 of the people killed were civilians.
In addition, an estimated 1.2m Iraqis have been displaced by fighting, including from Anbar and Ninewa governorates, according to the UN Refugee Agency