The Nigerian schoolgirls captured by Boko Haram last year could be freed under new negotiations between the government and the militant group.

Speaking on condition of anonymity, a human rights activist close to the negotiators told the Associated Press that talks to release the girls in exchange for Boko Haram leaders held by the government have been reopened.

Last year, reports emerged that the International Committee of the Red Cross was negotiating a prisoner swap and had been coordinating secret talks between the Islamist group and the Nigerian government.

However, the talks broke down and 219 girls remain in captivity, more than a year since their abduction from a school in Chibok, Borno State.

One of the current negotiators, Fred Eno, told AP that "another window of opportunity" has opened in the last few days. An increase in recent attacks by Boko Haram is an attempt to create a stronger position for negotiations, he added.

According to AP, Presidential adviser Femi Adesina said on Saturday that the government had not ruled out further talks with the militants. "Most wars, however furious or vicious, often end around the negotiation table," he said.

276 girls were abducted from their school in Chibok, northern Nigeria on April 14. Their plight gained international attention, with the hashtag #BringBackOurGirls trending on Twitter and politicians, celebrities and activists calling for their release.

Witnesses have recently claimed that at least some of the Chibok girls have been "brainwashed" by Boko Haram, and are carrying out murders on behalf of the group.