Nigeria's army on Sunday said it had freed more than 5,000 people held by the militant group Boko Haram during an operation over the weekend in the northeast of the country.

Nigeria's army has over the last year, sometimes aided by troops from neighbouring countries, recaptured most of the territory that was lost to the group, which has waged a seven-year insurgency aimed at creating a state in the remote northeast.

The army said troops, supported by members of a grassroots security force, conducted raids in 15 villages on Sunday, during which they "killed six Boko Haram terrorists and wounded several others".

"The troops also liberated over 5,000 persons held hostages by Boko Haram terrorists," it said in an emailed statement. Reuters could not immediately independently verify the freeing of the hostages, in part due to the remoteness of the area in which the military operation took place.

More than 15,000 people have been killed and 2 million displaced in Nigeria and neighbouring Chad, Niger and Cameroon during Boko Haram's insurgency.

However, the group, which last year pledged loyalty to Daesh organization, still regularly stages suicide bombings, mainly in crowded areas such as markets and places of worship.