The Nigerian army said it has captured the strategically significant town of Gwoza from Boko Haram.
Making the announcement on social media, the army said it had killed several members of the group and that a "mop-up" was now underway.
Nigerian media are reporting that more than two hundred of the girls captured in Chibok in April 2014 are being held in the town, in Bornea State.
A 56-year-old woman who was kidnapped by the group in 2014 and held in two locations by the group told the International Centre for Investigative Reporting that she was held along with the girls under very tight security in a house in Gwoza.
The town was first captured by Islamist fighter last year, and was declared the headquarter of the group's Caliphate.
Residents have said Boko Haram militants have kidnapped more than 400 women and children from the northern Nigerian town of Damasak that was freed this month by troops from Niger and Chad.
"They took 506 young women and children (in Damasak). They killed about 50 of them before leaving," a trader called Souleymane Ali told Reuters in the town.
"We don't know if they killed others after leaving, but they took the rest with them."
Troops from Niger and Chad last week found the bodies of at least 70 people in an apparent execution site under a bridge leading out of Damasak, where the streets remain strewn with debris and burnt-out cars after the fighting.
Armed forces from Chad and Niger have teamed up to launch a fresh offensive against Islamist militant group Boko Haram in Nigeria.
Troops entered the country through southeast Niger and attacked militants in Nigeria's Borno State.
We can confirm that Chadian and Nigerian forces launched an offensive this morning from Niger. The offensive is underway.
It comes after Boko Haram pledged allegiance to Islamic State, which has taken over parts of Iraq and Syria.
Nigeria's militant Islamist group Boko Haram has pledged allegiance to Islamic State, which rules a self-declared caliphate in parts of Iraq and Syria, according to an audio statement.
In a message believed to be from leader Abubakar Shekau the group said: "We announce our allegiance to the Caliph ... and will hear and obey in times of difficulty and prosperity".
Boko Haram has been waging a six-year military campaign to carve out an Islamic state in northern Nigeria.
Today four bomb blasts killed at least 50 people in the north eastern Nigerian city of Maiduguri in the worst attacks there since Boko Haram militants tried to seize the town in two major assaults earlier this year.
A third blast hit the northeastern Nigerian city of Maiduguri, according to a Reuters witness.
A military source said the first two explosions were from bombs, one in a market and another close to a market. The three blasts came in a period of just over half an hour. There was no immediate word on casualties.
An US missionary who was kidnapped in central Nigeria in February has been safely released to authorities and church leaders, her Free Methodist Church said in a statement.
Reverend Phyllis Sortor, a Free Methodist missionary to Nigeria, was safely released in Nigeria on Friday evening local time into the care of authorities and church leaders, the church said. She was abducted on February 23.
Simultaneous bombs have exploded at a bus station and opposite a university in the central Nigerian city of Jos, a witness has told Reuters news agency.
"There was a loud explosion opposition the university along the Bauchi road, and another one at the Bauchi road motor park," Garba Musa, a newspaper vendor along the road, told Reuters by telephone.
At least 26 people have been killed and dozens injured in suicide bomb attacks at two different bus stations in Nigeria.
In the first blast in the town of Potiskum, a man ran onto a bus and detonated the explosive, killing himself and 16 others and destroying the bus.
Two bombers then targeted a major bus station in the Nigeria's main northern city, Kano, in a coordinated attack which left at least 10 dead.
Nobody has yet claimed responsibility for the attacks, but officials believe they may be a sign of revenge from Islamist militant group Boko Haram following a strong of successful assaults from neighbouring countries.
At least 10 people died in a blast at a bus station in the northeast Nigerian city of Potiskum, a hospital source told Reuters.
Nigerian forces backed by air strikes have killed more than 300 Boko Haram fighters during an operation to recapture 11 towns and villages since the start of the week, the military said today.
"Several weapons and equipment were also captured and some destroyed," defence spokesman Major-General Chris Olukolade said in a statement.
The news follows a number of recent attacks by Boko Haram militants on civilians in Nigeria's border regions.