The United Nations says that a Chadian peacekeeper in northern Mali has killed two colleagues and injured another after shooting at them.

The spokeswoman for the U.N. mission in Mali, Radhia Achouri, said Sunday that authorities have arrested the soldier who fired in the Saturday night shooting in Tessalit in Mali's northern Kidal region. She said the reason for the attack was not known and that investigations have been opened into the incident.

This is the not the first time a Chadian soldier has opened fire on colleagues. On Feb. 25 in Kidal, a Chadian peacekeeper killed a commander and a doctor with the U.N. mission in Mali.

The U.N. mission in Mali, in the country since July 2013, has been one of the world body's deadliest peacekeeping missions.