BUJUMBURA, Burundi (AP) — Civic groups in Burundi on Tuesday rejected a U.N. facilitator of talks between the government and those opposed to a third term for President Pierre Nkurunziza, saying they feel he backs the president.

Several civic groups have written a joint letter to U.N. Secretary-General Ban Ki-moon expressing opposition to the role of Algerian diplomat Said Djinnit, according to Pierre Claver Mbonimpa, a leading rights activist here.

A spokesman for Ban has already said the U.N. chief fully supports Djinnit’s efforts to end Burundi’s political crisis.

Willy Nyamitwe, a presidential spokesman, said Tuesday the rejection of Djinnit is evidence of the opposition’s “lack of maturity.”

Burundi has been hit by political unrest since the announcement April 25 that Nkurunziza would seek a third term in office, which many see as unconstitutional. The country’s constitutional court has ruled in favor of him, however.

Protesters say Nkurunziza’s bid for a third term is illegal because the constitution only allows for two five-year terms after popular elections. Some protesters are vowing to stay on the streets until Nkurunziza says he will not run. At least 20 civilians have been killed in clashes with police who have used a combination of tear gas, water cannon and live ammunition.

A youth militia, the Imbonerakure, affiliated with the ruling party is accused of harassing opponents.

Zeid Raad al-Hussein, the U.N. human rights chief, said Tuesday the Imbonerakure’s 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.

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