A former British prime minister and United Nations special envoy for Global Education, Mr Gordon Brown, has issued a fresh plea to the kidnappers of 220 Chibok schoolgirls to release them immediately.

He urged the Boko Haram militants to free the girls who were taken from the town of Chibok last April.

Mr Brown was speaking after the same terrorist group on Thursday released 158 women and children taken during a separate raid on Katarko, in December. They were held captive for more than a month before finally being freed and reunited with their families.

In a statement signed by the United Nations information officer, Oluseyi Soremekun, he said, “though the circumstances of their release are still unclear, it could spark hopes that the Chibok girls can finally be returned home”.

Mr Brown said families had suffered 10 months of “cruelty and anguish” not knowing their fate.

Despite a worldwide campaign of ‘Bring Back our Girls’, their whereabouts remain unknown.

He recalled that, “the last clue to where they might be was a heartbreaking but chilling picture of the girls huddled together on scrubland, all wearing black and grey hijabs. It was taken just weeks after the kidnapping and sent to news agencies by Boko Haram”.

Mr Brown promised that there would be no let up in the campaign to find them and free them.

“I am making a humanitarian plea after the terrorists released a separate group of women and girls following a kidnapping that took place in December. Now they have released some hostages, they should release them all”.

“Boko Haram are piling cruelty upon cruelty by failing to free the girls. They have now been away from their families for 10 months”.

He assured that, “we will keep up pressure until they are released and if they are still prisoners, we will mark the one year of captivity with a vigil planned at the United Nations in New York on April 14”.