Up to 50 Chibok schoolgirls released by Islamist Boko Haram militants

Twenty-one of the Chibok schoolgirls kidnapped by Boko Haram more than two years ago were freed on October 13, 2016. Photo / Getty Images

Up to 50 Chibok schoolgirls have been released by Islamist Boko Haram militants after more than three years in captivity, a Nigerian government spokesman says, the largest group yet to be freed after years of negotiations.

An earlier report said 82 girls had been freed.

The girls were among about 220 students abducted from a secondary school in the northeastern town of Chibok in 2014, sparking a global campaign #bringbackourgirls supported by then US First Lady Michelle Obama and a list of celebrities.

About 21 Chibok were released in October in a deal brokered by Switzerland and the International Red Cross, while a handful of others have escaped or been rescued. But about 195 were still missing.

"The government will soon release an official statement," a government spokesman told the Thomson Reuters Foundation.

Last month President Muhammadu Buhari said in a statement that the government was "in constant touch through negotiations, through local intelligence to secure the release of the remaining girls and other abducted persons unharmed".

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

-AAP