The fighting happened Thursday in the Sambisa Forest Reserve, just south of Maiduguri, the capital of Borno state, which soldiers previously targeted hunting for fighters belonging to the extremist network known as Boko Haram. Details of the raid, however, remained sketchy on Friday as a military spokesman offered contradictory details about the assault.
Meanwhile, gunmen launched an assault on the hometown of one of Nigeria's former military rulers hundreds of miles (kilometers) away, attacking police stations and banks.
Soldiers started the attack on Sambisa Forest Reserve on Thursday, having previously converged on the area in advance of President Goodluck Jonathan's state of emergency decree affecting three states in the nation's northeast, a security official said. The shelling with cannons killed at least 21 suspected Islamic extremists, the official said. There was no independent confirmation of the assault or casualties.
"We are not going to leave the forest until it's over," the official said, referring to the emergency rule.
The official spoke to The Associated Press on condition of anonymity since he was not authorized to speak publicly about the ongoing military operation.
Brig. Gen. Chris Olukolade, a military spokesman based in Abuja, Nigeria's capital, told the BBC on Friday that the military conducted air strikes on "enclaves in the forest, the deep forest," where insurgents were hiding. Olukolade also said that insurgent fire hit one of the military's aircraft, causing it to abandon the fight and return to a nearby airfield.
However, when Olukolade later spoke with The Associated Press, he said he was "not certain" if airstrikes had been carried out. Read back portions of his comments to the BBC, the brigadier general said: "I don't want to talk about that."
"This is my position at the moment," he said. He declined to discuss casualty figures from the fighting.
A written statement attributed to Olukolade issued Friday night said soldiers destroyed heavy weapons such as anti-aircraft guns and anti-tank weapons, as well as vehicles, generators and other equipment. "The Defense Headquarters is quite satisfied with the progress of the operation and the fighting spirit of participating troops," the statement read.
Under the president's directive, soldiers have ultimate control over security matters in Adamawa, Borno and Yobe states. Over the last few days, witnesses and AP journalists have seen convoys of soldiers in trucks and buses moving through the region, as well as trucks carrying armored personnel carriers. Jet fighters also have been seen flying low over Yola, the capital of Adamawa state. Soldiers shut down the state's border crossings Friday with neighboring Cameroon as part of the security crackdown.
This new military campaign comes on top of a previous massive deployment of soldiers and police to the region. That deployment failed to stop violence by Islamic extremists, who have killed more than 1,600 people since 2010, according to an AP count. It also has seen soldiers arrest, torture and even kill civilians.
In a statement Friday, U.S. Secretary of State John Kerry said his nation remained "deeply concerned" about the fighting in northeast Nigeria.
"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," the statement reads. "The United States condemns Boko Haram's campaign of terror in the strongest terms. We urge 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."
Meanwhile, oil-rich Nigeria suffers from continued insecurity throughout the country, whether it be kidnappings in its east, oil pipeline thefts in its southern delta, or violence by ethnic militias throughout its fertile central belt.
That could be seen Thursday night in Daura, a rural town in Katsina state that's the home of former military ruler and perennial presidential candidate Gen. Muhammadu Buhari. There, far from the states under emergency rule, gunmen attacked police stations and at least four banks, witnesses said. At least two soldiers and five suspected insurgents were killed in the fighting, according to statements from the police and the military.
After the attack, Maj. Gen. Bola Koleosho told journalists in Abuja that Islamic fighters are using camouflage uniforms, similar to those worn by government troops, to perpetrate violence against civilians and to create an impression that it was carried out by government forces. Islamic extremists have raided military barracks in the past and displayed uniforms, weapons and bulletproof vests as trophies in propaganda videos.
Also Friday, mobile phone service returned to parts of northeast Nigeria after being cut Thursday. The security official told the AP that the service cut came on the orders of Nigeria's government and security forces as soldiers moved into the northeast to begin operations. The official said service likely would be shut off again.
Mobile phones have become the only real communication device in Nigeria for both voice calls and the Internet, as the state-run telephone company collapsed years ago. By cutting off service at towers, the military could stop extremists from receiving warnings or intelligence ahead of their operations. Authorities said Thursday they had no information about the service cutoff or refused to comment.
Nigeria's military and security forces have tracked fighters by their mobile phone signals in the past as well, prompting extremists from Boko Haram to attack mobile phone towers in the region.
Associated Press writers contributing to this report include Bashir Adigun in Abuja, Nigeria; Ibrahim Abdul in Yola, Nigeria; and Muawiya Garba Funtua in Katsina, Nigeria.
Jon Gambrell reported from Yenagoa, Nigeria, and can be reached at www.twitter.com/jongambrellAP.