In his first speech as U.N. human rights chief, Zeid al-Hussein has called Syria a "slaughterhouse" and the Islamic State group sprung from the civil war's chaos an unprecedented force of violence against ethnic and religious groups.

The veteran diplomat and campaigner for international justice says the world's first urgent priority should be to halt the increasingly conjoined conflicts in Iraq and Syria.

Zeid, who is the first U.N. human rights chief from the Muslim and Arab worlds, also told the U.N. Human Rights Council on Monday that at least 3,000 people were killed since mid-April in Ukraine.

His four-year post began Sept. 1. He previously served as Jordan's U.N. ambassador and ran for secretary-general before Ban Ki-moon was chosen for the job.