The U.N. peacekeeping mission in Mali says a peacekeeper has shot dead two colleagues in what has been called a "settling of scores."

A statement from the mission Friday says the suspect was immediately detained after the shooting Thursday at the U.N. base in Kidal in northern Mali. An investigation is under way.

A peacekeeping official says the Chadian peacekeeper shot a commander and doctor. The official spoke on condition of anonymity because the official was not authorized to speak publicly.

It was not clear what caused the shooting.

Mission spokesman Olivier Salgado says operations at the base have returned to normal.

The U.N. mission in Mali has been one of the world body's deadliest peacekeeping missions.

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Associated Press writer Baba Ahmed in Bamako contributed.