Flights from the Malian capital, Bamako, to the northern cities of Timbuktu and Gao have been cancelled because of insecurity.
Several shells landed near Timbuktu airport on Monday. A United Nations camp was hit.
Malian authorities reportedly imposed a 30-day curfew on Timbuktu on Monday. The city has been under a blockade for the past month after Islamist militants cut off road and river routes.
There are concerns of further instability as thousands of UN peacekeepers pull out of the country following a request by the military rulers who seized power in a coup.
Both Timbuktu and Gao have also seen fighting between the army and predominantly Tuareg rebels.