The ongoing violence and chaos in Iraq has killed nearly 15,000 civilians and wounded 30,000 over a 16-month period that ended on April 30, according to a United Nations report released Monday.

Iraq is engaged in a conflict with extremist groups, reportedly its worst since the 2011 withdrawal of American forces. Several major Iraqi cities, including Mosul and most of Anbar province, have fallen to the Islamic State group, which is locked in combat throughout the country with Iraqi security forces.

The U.N. report blames the disastrous death toll on ISIS, which may have committed war crimes, crimes against humanity and genocide during its brutal rise to power in the country's northern and western regions.

The U.N. mission in Iraq and the U.N. human rights authority said in the report that over 2.8 million Iraqis also fled their homes during this period and remain internally displaced, including an estimated 1.3 million children.

Although much of the report focuses on ISIS' actions, it also found violations of human rights and international law by Iraqi security forces and their allies, including international troops and local militia. The report stated that they were accused of unlawful killings of those believed to be ISIS associates, and causing civilian deaths in airstrikes.

The report collected many examples of killings, attacks or abductions carried out by ISIS militants against their opponents, which included ethnic and religious minorities, armed forces and police, government officials, lawyers, journalists and other professionals. It also cited several unverified reports, which claimed that ISIS used chlorine gas in its attacks.

The U.N. report also said that up to 3,500 members of the Yazidi and other minority communities remained in ISIS captivity, "where they are subjected to physical, sexual and other forms of violence and degrading treatment on a daily basis."

The report, however, did not break down who was responsible for the casualties.

The U.N. has also previously accused ISIS of taking "cultural cleansing" to "unprecedented levels in modern history" by destroying historical and cultural artifacts.