Fighting between armed groups and the army in northwest Nigeria has forced international aid group Medecins sans Frontieres (MSF) to evacuate some of its staff in the area, the agency said on Friday.

The move illustrates the difficulty humanitarian groups face in Nigeria's northwest, where militias known locally as bandits attack communities, loot villages and carry out mass kidnappings for ransom.

The MSF said an escalation of violence in Zamfara state prompted the agency to withdraw part of its staff from Zurmi town, where clashes occurred around the local hospital.