Nigeria's President Goodluck Jonathan has declared a state of emergency in three parts of his country following an increase in violence from Islamist groups.
The emergency rules apply to Borno, Yobe and Adamawa states in the northeast of Nigeria where Islamist sect Boko Haram is reported to have intensified its attacks on security forces and government targets.
"We are facing ... a rebellion and insurgency by terrorist groups which pose a very serious threat to our national unity," President Jonathan said in a televised address.
"They have attacked government buildings and facilities. They have murdered innocent citizens and state officials. They have set houses ablaze, and taken women and children as hostages. These actions amount to a declaration of war."
His orders followed growing evidence that Boko Haram now control parts of the northeastern territory around Lake Chad, where local government officials have fled.
Security officials say they control at least 10 local government areas of northeast Borno state, the heart of the uprising.
Dozens of Boko Haram fighters in buses and machine gun-mounted trucks attacked the town of Bama last week, freeing more than 100 prison inmates and leaving 55 people dead, mostly police and other security forces.
Days earlier, scores were killed in the fishing village of Baga, also in Borno, on the shores of Lake Chad, after troops from Nigeria, Niger and Chad raided it in the hunt for anti-government rebels.
Local residents said soldiers were responsible for many civilian deaths.
The decree is likely to bring him into conflict with the powerful governors and northern leaders, with whom he already has a tense relationship.
Boko Haram and other Islamist groups such as al Qaeda-linked Ansaru have become the biggest threat to stability in Africa's second biggest economy and top oil exporter.
The group's leader, Abubakar Shekau, said in a video this week that the group had kidnapped several women and children in retaliation against security forces who, it says, have detained the wives and children of its members without just cause.