New York - Unidentified gunmen attacked the headquarters of the UN peacekeeping force in the northern Mali city of Timbuktu on Monday, killing seven people and injuring seven others in what the UN peacekeeping chief called a "terrorist attack".Earlier Monday, gunmen attacked two neighboring UN camps in Douentza in the Mopti region of central Mali, killing a Malian soldier and a UN peacekeeper and lightly wounding another peacekeeper. The head of the UN peacekeeping mission in Mali, Mahamat Saleh Annadif, also called that incident a "terrorist attack".The UN peacekeeping mission in Mali is the deadliest of the UN's 16 global peacekeeping operations, and this was one of the worst losses of mission employees.In the Timbuktu attack, the mission said five Malian security guards and a Malian contractor working for the mission were killed along with a member of the Malian gendarmerie. It said six UN peacekeepers were wounded, two seriously, along with one Malian security guard.The mission, known as MINUSMA, said it dispatched a quick reaction force and attack helicopters to secure the Timbuktu headquarters. It said UN troops killed six assailants.In Douentza, MINUSMA said a group of attackers fired on a UN camp from an adjacent hill and Malian troops returned fire. Another armed group shot at peacekeepers in a neighboring camp who also returned fire, the mission said. The UN mission said two attackers were killed in the exchanges.Annadif, the MINUSMA commander, called for those responsible for "these terrorist attacks" to be arrested and brought to justice.