Suspected Boko Haram militants began attacking Nigeria's major northeastern city of Maiduguri just after midnight on Sunday, military, government and local sources said.

At around 9 am (0300 ET) on Sunday, a Reuters witness said shelling could be heard and that military helicopters were circling the city.

The militants began the attack at the edge of the city in the Njimtilo area. The city is the capital of Borno state and would be a major prize for the insurgents who are trying to carve out an Islamic state.