The U.N. human rights chief is voicing alarm over reports of violence and intimidation by a militia attached to the youth wing of Burundi's ruling party, the Imbonerakure.

Zeid Raad al-Hussein said Tuesday its actions "could tip an already extremely tense situation over the edge." He said his office has received "consistent testimonies" indicating that Imbonerakure members operate under instructions from the ruling party and with weapons, vehicles and sometimes uniforms provided by police and intelligence services.

Burundi has been hit by unrest since an announcement April 25 that President Pierre Nkurunziza would seek a third term, which many see as unconstitutional.

Zeid said Burundian authorities must "show their commitment to peace by clearly disassociating themselves from their violent supporters" and ensure they are brought to account for any crimes.