Nigeria's army has begun operations against militant Islamists in the north-east, military officials say.They say troops raided parts of a game reserve in Borno state where the Boko Haram group has established bases.
The raids came after states of emergency were declared in Borno, Yobe and Adamawa north-eastern states, where 2,000 people have died since Boko Haram launched an insurgency in 2009.
A dusk-to-dawn curfew has been imposed in Adamawa to curb militant attacks.
A BBC reporter in Adamawa says that decision is surprising, as the security situation there is less serious than in Borno and Yobe. On Thursday soldiers raided "terrorist camps" in the Sambisa Game Reserve, a remote 500 sq km (200 sq mile) savannah in Borno that is known to be a haven for Boko Haram militants, officials are quoted as saying.
Nigerian military spokesman Brig Gen Chris Olukolade said "every resource available" to the armed forces would be used against Boko Haram.
Correspondents says this means fighter jets and helicopter gunships are likely to be deployed.
Our reporter says the hardest part of this campaign will be in urban areas like the Borno state capital, Maiduguri, where the Islamist militants are living among the civilian population.
Mobile phone networks were not functioning in many parts of north-east Nigeria on Thursday, but our reporter says it is not clear if this is related to the current military offensive.
Militants have previously attacked mobile phone masts in the area in an effort to disrupt communications.
The BBC's Abdullahi Tasiu Abubakar in Adamawa city says many there feel the curfew is unnecessary and will disrupt their lives.
Our reporter adds that there is no sign of a huge military build-up in the city since President Goodluck Jonathan declared a state of emergency on Tuesday in the three states.
The president said the army would take "all necessary action" to "put an end to the impunity of insurgents and terrorists".
Boko Haram, whose name means "Western education is forbidden" in the local Hausa language, is fighting to overthrow the government and create an Islamic state in the north.
Although they often attack Christians and government targets, they have also killed many Muslim civilians.