Lagos, Nigeria (CNN) -- Hundreds of Boko Haram militants attacked an Air Force base and a military checkpoint in the northeastern Nigerian city of Maiduguri early Monday, according to government officials.
Loud explosions were heard between 3 and 4 a.m. and several ambulances were seen leaving the base. The number of casualties is unknown.
The governor of Borno state has imposed a strict 24-hour curfew forcing citizens to remain indoors and all air traffic in the state has been halted.
Borno is one of three embattled states in northeastern Nigeria that have been under a state of emergency since May as the region is the hotbed for Boko Haram Islamists trying to impose a strict version of Sharia, or Islamic law.
Last week Human Rights Watch said Boko Haram has abducted scores of women and girls and used children as young as 13 in their campaign of violence. The report says Boko Haram has killed 3,000 people since 2009.
CNN's Susanna Capelouto contributed to this report.