At least 30 militants have been killed during air raids on their training camps in north-eastern Nigeria, officials say. An army spokesman said jets and helicopter gunships had been used to attack several camps.
He told the BBC that a plane had been hit by anti-aircraft fire but had managed to return to base. States of emergency were declared this week in three north-eastern states hit by Boko Haram's Islamist insurgency.
Nigerian forces are trying to regain control in the states of Adamawa, Yobe and Borno. Meanwhile, explosions and gunfire have been heard overnight in Katsina state.
Residents have told the BBC's Hausa service that banks, police stations and prisons were destroyed in the town of Daura, near the border with Niger. They said they had seen the bodies of five members of the security forces and three militants, but there has been no official confirmation of casualties. Mobile phone networks were not functioning in many parts of north-east Nigeria on Thursday.
A security official told the AP news agency that the mobile phone service had been shut down during the military operation. Militants have previously attacked mobile phone masts in the area in an effort to disrupt communications. Some of the camps hit by air raids were in the Sambisa Game Reserve, about 70km (45 miles) south of the Borno state capital, Maiduguri, where the militants first emerged in 2009, said Nigerian military spokesman Brig Gen Chris Olukolade.
He told the BBC that 30 militants had been killed since the latest offensive began on Wednesday. There is no independent confirmation of the number of deaths. The aim is to "destroy [Boko Haram] bases, apprehend as many of them as possible and bring them to justice", Brig Gen Olukolade said.
"It is not just Sambisa, every camp is under attack," the Reuters news agency quoted him as saying. In January, the military said it had deployed helicopter gunships to destroy Boko Haram camps in the reserve, not far from Bama, where 55 people were killed in militant attacks last week.
Brig Gen Olukolade said the plane damaged by anti-aircraft fire had returned to base safely, while the "terrorist base" was subsequently "completely destroyed". This is the first time Boko Haram has been reported to have used such heavy weaponry against aircraft.
A Maiduguri resident told the BBC that the city was unusually quiet on Friday, with most people staying inside. Brig Gen Olukolade said "several thousand" troops had been sent to the three north-eastern states to tackle Boko Haram.
The three semi-desert states, which border Niger, Chad and Cameroon, are roughly the size of England or the US state of Illinois but have a population of just 10 million. The BBC's Will Ross in Abuja says targeting Boko Haram's rural bases or training camps should pose no great challenge for the military; the hardest part of this campaign will be in urban areas like Maiduguri, where the militants are living among the civilian population.
The president said the army would take "all necessary action" to "put an end to the impunity of insurgents and terrorists", saying they had taken down the Nigerian flag and replaced it with a foreign emblem in some parts of the country.
Human rights organisations have criticised some of the Nigerian military's previous operations because of the resulting civilian casualties. 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.