Nigeria's military says it has destroyed the headquarters of Boko Haram in Gwoza and expelled fighters from all three northeastern states that had formed the group's stronghold.
The country's armed forces have claimed a number of successes against the group in recent weeks but It was not possible to verify Friday's claim that comes the day before presidential elections.
Al Jazeera's Yvonne Ndege, reporting from the capital, Abuja, said opposition figures were sceptical of the claim Boko Haram had been expelled from Gwoza.
"The opposition say there have been restrictions placed on civil society, human rights organisations, and the media, in terms of accessing Gwoza and other towns the Nigerian military says they have liberated," she said.
"They say the timing of this announcement is way too suspicious."
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Defence spokesman Major General Chris Olukolade said several fighters were killed, many captured, and a "massive cordon and search'' operation has started to hunt down fleeing fighters and any hostages, the Associated Press news agency reported.
Defeated fighters are believed to be heading to the borders, where troops from a multinational force are preparing to engage them, he said.
Boko Haram leader Abubakar Shekau declared Gwoza the capital of a new "Islamic caliphate" after the group seized the town in August.
There was no mention in the defence ministry's statement of the Sambisa Forest, where Boko Haram is believed to have several camps. Warplanes have been bombing the area for weeks.
The forest starts about 30km from Gwoza town, which is 130km southeast of Maiduguri, the capital of Borno state and birthplace of Boko Haram.
At least 10,000 people were killed in the uprising last year and more than 1.5 million people have been driven from the homes.
Source: Al Jazeera And AP