Boko Haram militants released 82 schoolgirls who were kidnapped more than three years ago.

Saturday's release was the largest group to be freed after years of tense negotiations.

In April 2014, about 220 students were abducted from a secondary school in the northeastern town of Chibok -- sparking a global recovery effort campaign.

About 21 schoolgirls were released in October of last year in a deal brokered by Switzerland and the International Red Cross, while a handful of others have escaped or been rescued, dozens remain missing.

The girls were taken from a school where Boko Haram has waged an insurgency aimed at creating an Islamic state that has killed thousands and displaced more than 2 million people.