The U.N. human rights chief is warning that a "large-scale crisis could be just around the corner" in Congo, where dozens of people have been killed this week in protests against a delayed presidential election.

Zeid Ra'ad al-Hussein said in a statement Thursday that Congo's authorities "need to pull back from their extremely confrontational position" after the headquarters of several opposition parties were burned.

Zeid says some civilians were killed by gunshots to the head or chest and condemns the "excessive use of force" by security officials. He also condemns attacks by "unknown assailants" against the ruling party headquarters.

Some see the delay of Congo's election, originally set for November, as an attempt by President Joseph Kabila to stay in power beyond the end of his mandate in late December.