More than 130 members of the Boko Haram terrorist group have surrendered to Nigeria's military.

Mohammed Bashir, a man who had posed as the group’s leader Abubakar Shekau in numerous videos, was also been killed in clashes, the military said on Wednesday.

Defence spokesman Major-General Chris Olukolade said: “In the course of those encounters, one Mohammed Bashir, who has been acting or posing on videos as the deceased Abubakar Shekau ... known as leader of the group, died.”

Following the surrender, Nigeria's military has released photographs of dozens of detainees sitting on the floor and the alleged body of the leader.

Over the past five years, the group has killed thousands of people in guerrilla attacks on military installations and against civilians. In the past two months, its ambitions have grown as it has started to seize and hold ground in Nigeria.

After members of the extremist group seized several small towns and declared the area an Isis-style ‘Islamic Caliphate’, Nigeria’s army stepped up its military operations in the rural northeast.

The Nigerian army said that 135 Boko Haram fighters had handed their weapons to troops on Tuesday in the town of Biu, near the epicentre of Boko Haram’s campaign to carve out an extremist Islamist state.

Reports from BBC News citing the country’s military claimed the number was as high as 260, as a further 133 members reportedly surrendered in north-eastern Nigeria.

Last August, Nigeria's military said Shekau may have died of gunshot wounds some weeks after a clash with soldiers.

Following the reports, the man appearing in Boko Haram videos appeared to look different, with a rounder, less narrow face and a wider nose.

In pictures: Nigeria kidnapped schoolgirls Show all 35 1 /35 In pictures: Nigeria kidnapped schoolgirls In pictures: Nigeria kidnapped schoolgirls Nigeria A total of 276 girls were abducted from the northeastern town of Chibok, in Borno state, which has a sizeable Christian community. Some 223 are still missing In pictures: Nigeria kidnapped schoolgirls Nigeria One of the kidnapped girls looks into a camera In pictures: Nigeria kidnapped schoolgirls Nigeria One of the missing girls talking to the camera In pictures: Nigeria kidnapped schoolgirls Nigeria The missing Nigerian schoolgirls, wearing the full-length hijab and praying in an undisclosed rural location. Boko Haram alleging they had converted them to Islam In pictures: Nigeria kidnapped schoolgirls Nigeria Girls wearing the full-length hijab holding a flag reading "There is no god, but Allah" and "Mohammed is Allah's prophet" In pictures: Nigeria kidnapped schoolgirls Nigeria A man claiming to be the leader of Nigerian Islamist extremist group Boko Haram Abubakar Shekau In pictures: Nigeria kidnapped schoolgirls Nigeria Abubakar Shekau speaks on the video In pictures: Nigeria kidnapped schoolgirls Nigeria Girls, wearing the full-length hijab and praying are filmed by an unidentified man (R) in an undisclosed rural location In pictures: Nigeria kidnapped schoolgirls Nigeria Soldiers lead the way as Chibok residents carry placards to protest the abduction of the missing schoolgirls in Maiduguri In pictures: Nigeria kidnapped schoolgirls Nigeria People carry signs as they attend a protest demanding the release of abducted secondary school girls in the remote village of Chibok in Lagos In pictures: Nigeria kidnapped schoolgirls UK Demonstrators hold banners as they protest about the kidnapping of girls in Nigeria, near the Nigerian High Commission in London In pictures: Nigeria kidnapped schoolgirls UK A protester demonstrates against the kidnapping of school girls in Nigeria, outside the Nigerian Embassy in London In pictures: Nigeria kidnapped schoolgirls UK Chief International Correspondent Christiane Amanpour and Prime Minister David Cameron appearing on the BBC1 current affairs programme In pictures: Nigeria kidnapped schoolgirls USA People participate in a "Bring Back Our Girls" campaign demonstration and candlelight vigil in Los Angeles In pictures: Nigeria kidnapped schoolgirls USA Girls holding heart shaped banners in a "Bring Back Our Girls" campaign demonstration and candlelight vigil in Los Angeles In pictures: Nigeria kidnapped schoolgirls South Africa South Africans protest in solidarity against the abduction of hundreds of schoolgirls in Nigeria by the Muslim extremist group Boko Haram and what protesters said was the failure of the Nigerian government and international community to rescue them, during a march to the Nigerian Consulate in Johannesburg In pictures: Nigeria kidnapped schoolgirls South Africa The kidnapping has ignited a viral social media campaign that has brought renewed attention to Boko Haram's campaign of violence, and protests around the world In pictures: Nigeria kidnapped schoolgirls South Africa Some of the hundreds of protests demonstrate outside the Nigeria Consulate to bring attention to the girls abducted in Nigeria, Johannesburg In pictures: Nigeria kidnapped schoolgirls South Africa South Africans from various civil society organisations protest in support of the Nigerian abducted Chibok school girls outside the South African parliament in Cape Town In pictures: Nigeria kidnapped schoolgirls Sri Lanka Participants chant slogans and hold placards during a protest to demand the return of hundreds of school girls abducted by the Boko Haram separatist group at the World Conference on Youth 2014, hosted by Sri Lanka in Colombo In pictures: Nigeria kidnapped schoolgirls USA Karilyn Coates (10) joins others in a candlelight vigil for the more than 300 girls abducted by Boko Haram in Nigeria, at All Souls Unitarian Church in Colorado Springs In pictures: Nigeria kidnapped schoolgirls USA Mia Kuumba, of the District of Columbia, brandishes a wooden stick during a rally in front of the Nigerian embassy in northwest Washington In pictures: Nigeria kidnapped schoolgirls Nigeria Mothers of the missing Chibok school girls abducted by Boko Haram Islamists gather to receive informations from officials. Nigeria's president said that Boko Haram's mass abduction of more than 200 schoolgirls would mark a turning point in the battle against the Islamists, as world powers joined the search to rescue the hostages In pictures: Nigeria kidnapped schoolgirls Nigeria Nana Shettima, the wife of Borno Governor, Kashim Shettima (C) weeps as she speaks with school girls from the government secondary school Chibok that were kidnapped by the Islamic extremist group Boko Haram, and later escaped in Chibok In pictures: Nigeria kidnapped schoolgirls Nigeria Leader of Chibok community in Abuja Hosea Sambido (R) raises a newspaper reporting the death of two of the abducted Chibok school girls during a rally pressing for the girls' release in Abuja, ahead of World Economic Forum In pictures: Nigeria kidnapped schoolgirls Nigeria Femi Falana, a lawyer and human rights activist (C) leads a mass-demonstration calling on the government to increase efforts to rescue the hundreds of missing kidnapped school girls of a government secondary school Chibok in Lagos In pictures: Nigeria kidnapped schoolgirls Nigeria Members of Lagos based civil society groups shout slogans calling for the release of missing Chibok school girls at the state government house in Lagos In pictures: Nigeria kidnapped schoolgirls Nigeria The Islamist group Boko Haram has claimed responsibility for abducting over 200 girls from their school in Chibok, Borno state. Nigerian police offered a reward of 50 million naira (about 310,000 US dollar) to anyone providing a lead on the whereabouts of the more than 200 school girls abducted by Islamist extremist group Boko Haram. Nigerian President Goodluck Jonathan has accepted an offer of help from the United States in tracking down and fighting the terrorists, US officials said In pictures: Nigeria kidnapped schoolgirls Nigeria Nigerians protest over the government's failure to rescue the abducted Chibok school girls in Port Harcourt In pictures: Nigeria kidnapped schoolgirls Nigeria Former Nigerian Education Minister and Vice-President of the World Bank's Africa division (3rd L) Obiageli Ezekwesilieze speaks as she leads a march of Nigeria women and mothers of the kidnapped girls of Chibok, calling for their freedom in Abuja In pictures: Nigeria kidnapped schoolgirls Bring Back Our Girls Michelle Obama tweeted a picture of her supporting the #BringBackOurGirls campaign Twitter In pictures: Nigeria kidnapped schoolgirls Bring Back Our Girls Malala joined calls for the kidnapped girls to be found Twitter/Malala Fund In pictures: Nigeria kidnapped schoolgirls Bring Back Our Girls Leona lewis supports #BringBackOurGirls campaign In pictures: Nigeria kidnapped schoolgirls Bring Back Our Girls Kelly Hoppen tweeted: 'Please make sure you do this, we must stand together and not forget them' In pictures: Nigeria kidnapped schoolgirls Bring Back Our Girls E.L. Rock Star tweeted: 'Join The Movement'

As the group has transformed from a radical but relatively peaceful clerical movement to an insurrection, Shekau had appeared in a number of videos issuing threats and taunting the authorities.

In one such clip, he claimed responsibility for the abduction of 200 schoolgirls from the remote village of Chibok in April, which sparked an international outcry and the '#BringBackOurGirls' social media campaign. The majority remain in captivity.

The surrender comes after one of the more than 200 schoolgirls abducted was freed this week, according to police and a parent of some of the other missing girls.

She is receiving medical attention after she was found running in a village, having spent four days in the bush, said a parent, who has two girls still with the insurgents and who declined to be named.