More than 700 people abducted by the armed group Boko Haram in Nigeria have escaped from captivity, according to a spokesman for the army.

The captives included farmers, fishermen and members of their families, Colonel Timothy Antigha said in a statement on Facebook on Monday.

Boko Haram had kept the villagers as "farm workers" on various islands in Lake Chad, he said, adding that the escapees were found by Nigerian troops near the northeastern town of Monguno, close to Nigeria's border with Chad.

Two women from the group have since given birth at an army base in Monguno, Antigha said.

Over 700 farmers and fishermen regain freedom as Boko Haram structures collapse pic.twitter.com/YuWMwa2Ze2 — Nigerian Army (@HQNigerianArmy) January 1, 2018

Boko Haram, whose name roughly translates to "Western education is forbidden", has waged an armed campaign to create an Islamic state in northeastern Nigeria.

The eight-year conflict has left at least 20,000 people dead and displaced more than 2.6 million.

Boko Haram gained international notoriety after its fighters kidnapped more than 200 schoolgirls in the town of Chibok. About 100 girls are still missing.

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At its peak, the group controlled large swaths of territory in the Lake Chad region, but the Nigerian military, with assistance from Chad, Cameroon and Niger, has pushed Boko Haram fighters out of a number of provinces in the northeast.

Antigha attributed the escape of the more than 700 hostages on Monday to military operations in the area, which were "targeted at destroying Boko Haram infrastructure and logistics, such as communication centres, fabrication yards, bomb-making equipment, vehicles and other means of sustenance".

Al Jazeera's Ahmed Idris, reporting from Nigeria's capital, Abuja, said the latest discovery came almost a year after President Muhammadu Buhari's administration announced that Boko Haram had almost been defeated.

"Since that announcement, we have seen daring and sometimes devastating attacks by Boko Haram fighters in the northeast and they have taken a lot of people hostage," he said.

"The army is continuing its operations, but Boko Haram has proven to be a resilient force in northeastern Nigeria," he added.