A local government administrator, a local chief, another elder and a resident all said some 300 children were among the 500 girls, boys and women taken from Damasak on Monday November 24, 2014.
The numbers involved surpass even the 276 schoolgirls who were taken from Chibok in April the same year, which drew worldwide condemnation and calls for action.
But the government of former president Goodluck Jonathan in March last year denied reports of the Damasak kidnapping while a local senator and a senior intelligence source also doubted the claim.
"Every parent was afraid to speak out," he said on condition of anonymity.
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Locals who managed to flee alerted their political representatives in the Nigerian Senate and House of Representatives but "they kept mute and ignored us", he added.
"The government didn't want the news out," he said, explaining the decision to speak out publicly came after Human Rights Watch highlighted the case yesterday.
"They also went into town and forcibly seized children from their mothers, children too old to be breastfed. My 16 nephews were among the children kidnapped. They were aged between five and 16."
Hundreds fled across the river that separates Damasak from Diffa in neighbouring Niger but many drowned, he said, adding that he returned to bury "over 200 dead bodies in mass graves".
The Damasak elder said the insurgents killed more than 200 in the initial attack, which happened on market day.