The U.N. human rights chief says many people in Burundi are living in "terror" with increasing reports of torture, almost daily grenade attacks, arbitary arrests and killings while the perpetrators go unpunished.

Zeid Ra'ad Al Hussein told the U.N. Security Council on Friday that "the country remains on the brink of a sudden escalation of violence to even more massive proportions."

He said some positive signals by the government in recent weeks following high-level visits including by the council and U.N. secretary-general "have yet to be followed up with strong and consequential action."

More than 400 people have been killed in Burundi's current unrest which started in April when it was announced that President Pierre Nkurunziza would seek a third term, which he won.