The U.N. human rights chief is calling for an international investigation of human rights violations in Yemen's civil war, which has killed thousands.

Zeid Ra'ad al-Hussein's call came as his Geneva office on Thursday released a 22-page report chronicling abuses on both sides in the war. The conflict pits the internationally recognized Yemeni government, backed by a Saudi-led coalition, against Shiite rebels known as Houthis and their allies.

Fighting escalated in March 2015 with the start of Saudi-led airstrikes.

The U.N. report also denounces the recruitment of child fighters in Yemen, suspected U.S. drone strikes and attacks on rights defenders.

Zeid's office says an estimated 3,799 civilians have been killed since the escalation of the conflict. The U.N. and rights groups estimate at least 9,000 people overall have died.