Zeid Raad al-Hussein told the UN Human Rights Council in Geneva on Thursday that many IS recruits "may genuinely feel they are signing up to protect the abused" because of propaganda.
Zeid says the fact the majority of the group's victims are Muslims has received less publicity and "a real campaign of ideas to discredit (IS) will need to mobilize such facts."
He says it should encourage the tolerant majority of Muslims "to take a stand and voice the essential nature of their faith."