Lagos — The mother of a kidnapped Chibok schoolgirl appealed on Monday for Nigeria's president to free detained Boko Haram militants in exchange for the more than 200 girls held captive, as the Islamic extremists have offered.A Boko Haram video posted on Sunday shows dozens of the 218 girls who were abducted from a remote school in April 2014, with one saying that "some" have died in military airstrikes.Nigeria's defence ministry disputed that. "It is extremely difficult and rare to hit innocent people during airstrikes because the operation is done through precision attacks on identified and registered targets and locations," spokesperson brigadier general Rabe Abubakar said in a statement.In the video, one of the kidnapped girls begs their parents to press Nigeria's government to free detained Boko Haram members so that the schoolgirls can be freed in a prisoner swap."The government should just release the militants," her mother, Esther Yakubu said. She wept when she watched the first proof of life of her daughter since her capture."All the girls that have been rescued have rescued themselves. Not any government has rescued them, no army rescued them," she said."We are being extremely careful"Dozens escaped on their own within hours of the mass abduction of 276 students that shocked the world. In May, a lone Chibok girl escaped from the Sambisa Forest stronghold of Boko Haram, saying she was led to freedom by her disillusioned Boko Haram "husband".The Bring Back Our Girls campaign is also pressing for a prisoner exchange, saying President Muhammadu Buhari "rode to power" on the back of their cause but has done nothing tangible to free the girls."Mr. Buhari can absolutely afford to trade terrorists' lives for schoolgirls," said human rights lawyer Emmanuele Ogebe, whose Education Must Continue campaign is paying to educate some of the escaped Chibok girls in the United States.He questioned the president's sincerity, noting that Buhari said in May that he had not watched a proof-of-life video sent by Boko Haram to encourage negotiations, apparently as early as January.Officials are wary, noting previous negotiations have failed because officials have been duped into talks with the wrong people."We are being extremely careful," Information Minister Lai Mohammed said in a statement. "We want to be doubly sure that those we are in touch with are who they claim to be."A fighter who speaks in the video hints at who could mediate. "We want the government to know that we don't trust you, except some few journalists. We have never sent out or accept to be approached by anybody except journalists that we trust."The video was posted on Sunday by Nigerian journalist Ahmad Salkida, who lives in Dubai and is known to have good contacts in Boko Haram. Salkida said the video was sent to him by Abubakar Shekau's wing of Boko Haram.On Sunday night, Nigeria's military declared Salkida a wanted man, claiming he has "information on the conditions and the exact location of these girls."