DAKAR, Senegal -- The Nigerian military stepped up its assault on Islamist militants in northeastern Nigeria, military officials said Friday, only days after the president announced a heightened campaign against insurgents who he said had declared war on the state.
Military officials said air and ground assaults were launched against suspected bases of the Boko Haram Islamist group in border areas at Nigeria's northeastern edge and in a forest south of the city of Maiduguri, the group's birthplace.
Officials said a number of insurgents had been killed in the raids but could not say how many. The military operation follows President Goodluck Jonathan's declaration of a state emergency in the country's northeast on Tuesday night, which followed heightened confrontations between Islamist militants and government security forces in that hard-hit region.
The president's speech, with its promise of a stepped-up military response to Boko Haram, prompted both critics and allies of the government to warn against further large-scale civilian killings by the army and the police, a pattern that has persisted since the start of the military's tough campaign against the Islamist insurgency nearly four years ago.
The United States gave some $3 million in law enforcement assistance to Nigeria last year, meets regularly with Nigerian officers on counterterrorism issues, and considers Nigeria a significant ally in the fight against Islamist extremism. But reports of civilian massacres by the military have made some officials in Washington uneasy.
On Friday, Secretary of State John Kerry said the United States was "deeply concerned about the fighting in northeastern Nigeria following President Jonathan's declaration of a state of emergency," and that "we are also deeply concerned by credible allegations that Nigerian security forces are committing gross human rights violations, which, in turn, only escalate the violence and fuel extremism."
Mr. Kerry made it clear that "the United States condemns Boko Haram's campaign of terror in the strongest terms," but he also urged "Nigeria's security forces to apply disciplined use of force in all operations, protect civilians in any security response, and respect human rights and the rule of law."
The scope of the current military operation appears somewhat larger than similar predecessors, although the northeast was already heavily militarized before the operation began, with numerous checkpoints on the region's roads, sandbagged military emplacements throughout Maiduguri and convoys of soldiers bristling with weapons regularly racing through the city's dusty streets.
"Advancing troops of Special Task Force have destroyed some terrorist camps sited in the forests of Northern and central Borno," said a statement from Nigeria's Defence Headquarters that was sent to reporters from the country's capital, Abuja, on Friday. "Heavy weapons including antiaircraft and anti-tank guns were also destroyed in the process."
"The special operations which preceded troops' movement has resulted in the destruction of much of the insurgents' weapons and logistics such as vehicles, containers, fuel dumps and power generators," the statement said, adding that "the casualties inflicted on the insurgents in the cause of the assault will be verified during mop-up."
An army spokesman, Brig. Gen. Chris Olukolade, said in a brief phone interview from Abuja that "the air force led the assault, helicopters and fighter jets," targeting "all the camps spread across border towns."
Critics wondered whether it would seriously disrupt the hit-and-run guerrilla insurgency of Boko Haram.
"We may win the battle but we may not win the war," said Kole Shettima, the chairman of the Center for Democracy and Development, a research organization in Abuja. The army "may succeed in disbanding some of the camps, but eventually, the insurgents being essentially mobile and nomadic in their activities, they will resurface," Mr. Shettima said. "They may even attempt to attack us in different parts of the country."
In Maiduguri, Islamist militants often come from and blend in with the civilian population, and in the extreme north, soldiers were conducting house-to-house searches for Boko Haram members, according to a military official in Maiduguri who was not authorized to speak publicly. The operations in the forested area to the south are proceeding with some difficulty, the official said, because the insurgents' camps are hidden by the trees.
He added that the forest had been "cordoned off" to forestall any attempts at escape.
Hamza Idris contributed from Bauchi, Nigeria.
This article originally appeared in The New York Times.