Isaac Rebecca, one of the girls who escaped from the Boko Haram camp, speaks during a protest last year held in Abuja to press for the return of the Chibok girls. Reuters

Nigerian extremist group Boko Haram is offering to free over 200 Chibok young women and girls who were kidnapped in exchange for the release of militants leaders held by the government, according to human rights activist.

The Associated Press reported that the group's offer only extends to the girls who were abducted en masse in northeastern Nigeria in April 2014. The girls' abduction led to a worldwide campaign called "Bring Back Our Girls".

The male activist, who was previously involved in negotiations with Boko Haram in 2014, asked to remain anonymous because he was not allowed to speak to reporters about the negotiations, the AP reported. Boko Haram's latest offer reflects the one made to the government of former President Goodluck Jonathan to release the 219 girls in exchange for 16 militant prisoners.

Nigerian negotiator Fred Eno confirmed to the AP that "another window of opportunity opened" in recent days but would not specify details. Eno told the AP that the militant group's recent increase in violence, including the murder of 350 people in the last nine days, reflects its struggle for a stronger position in negotiations.

The Nigerian government "will not be averse" to talking with Boko Haram, presidential adviser Femi Adesina said. He added: "Most wars, however furious or vicious, often end around the negotiation table."

The new government of President Muhammad Buhari is offering "a clean slate" to bring Boko Haram back to negotiations, which had been affected by several other security agencies. Eno told the AP that months-long negotiations in 2014 ended when the Department for State Service intelligence agency stopped a prisoner exchange.

The agency allegedly said it was only holding four of the prisoners Boko Haram was seeking in the exchange. However, the exact number of detainees held by Nigeria's intelligence agency is unknown. According to the AP, Amnesty International claims that 8,000 prisoners have died in military custody.

Boko Haram abducted 274, mostly Christian girls in the early hours of 15 April 2014. While dozens managed to escape within the first days of captivity, 219 remain abducted. In May 2014 the extremist group showed the girls in a video warning parents they would not see their daughters until their detainees were returned.

According to Reuters, President Buhari praised advocates of the "Bring Back Our Girls" for their continued efforts to bring continued focus on the missing girls at a meeting at his presidential villa in Abuja. "Nobody in Nigeria or outside could have missed your consistency and persistence," he said.

He added: "I think you will agree that the present government takes the issue very seriously."