Dozens of Nigerian women who were forced to marry Boko Haram fighters were reportedly slaughtered by their 'husbands' before a battle with troops in the northeast town of Bama. Witnesses said the Islamist militants feared they would be killed by advancing soldiers or separated from their wives when they fled the town. They killed the women to prevent them from subsequently marrying soldiers or other so-called non-believers, they said. Sharifatu Bakura, 39, said: 'The terrorists said they will not allow their wives to be married to infidels.' Scroll down for video . The leader of the Islamist extremist group Boko Haram Abubakar Shekau. The insurgents have lost ground to army forces in recent weeks . Nigeria's military, along with forces from neighbouring Cameroon, Chad and Niger have claimed huge victories over the insurgents in recent weeks but defenceless civilians still face serious threats. The Mother of three said Boko Haram fighters had got word of a military assault on Bama, formerly an Islamist stronghold in Borno state. The insurgents had decided to flee to the nearby town of Gwoza before the troops' arrival but first decided 'to kill their wives so that nobody will remarry them', she said. Mrs Bukara's husband was killed by the insurgents four months ago but she was spared from a forced marriage because she was visibly pregnant. Boko Haram forcibly married scores of women in Bama after seizing it in September but Nigeria's military announced its recapture of the town on Monday. Witnesses who were taken under military protection this week to Borno's capital Maiduguri, 45 miles away, said the killing of women began 10 days before Bama was liberated. The Islamists said 'if they kill their wives, they would remain pious until both of them meet again in heaven, where they would re-unite', said Salma Mahmud, another witness. A vigilante who fought alongside the military in the battle to retake Bama, Abba Kassim, said he saw 'dozens of women corpses' in the town. It has not been possible to verify exact numbers of those killed. Fanna Aisami, 52, also in Maiduguri after escaping Bama this week, said the executions followed a warning from Boko Haram's top commander in the town. 'He informed them of the situation and ‎the consequence of the takeover of the town by the advancing troops. 'He warned them that when soldiers killed them they would take their wives back to the society where they would be forced to marry and live with infidels,' said the mother of seven. The commander 'said it would be better for them to kill their wives and send them to heaven,' with number of women were shot dead in front of his house, she said. Advances: A photo released by the Nigerian Army shows soldiers in Goniri this week as forces claim a number of victories against the insurgents . Yagana Mairambe, 58, said some Boko Haram men refused and fled with their wives towards neighbouring Yobe state. Nigeria's national security spokesman Mike Omeri is working to verify the reports while the military could not immediately be reached for comment. With Boko Haram gunmen facing heavy military pressure across northeast Nigeria, attacks, including suicide bombings, have persisted, even as the government in Abuja tries to assure voters that March 28 elections will be secure. Security operatives search  for information at the main gate to the Monday Market where the blast occurred in Maiduguri, Nigeria, earlier this month . The Islamist uprising has claimed more than 13,000 lives since 2009 and President Goodluck Jonathan has faced fierce criticism over failure to contain the violence. The latest reported atrocities in Bama recall similar massacres at high schools and colleges across northeast Nigeria, where Boko Haram has executed scores of students learning a so-called infidel curriculum.
Fighters forcibly married women in Bama after seizing it in September . Women were killed amid fears they would be separated as they fled . Boko Haram fighters did not want them going on to marry 'non-believers'
Nigerian forces have recently claimed big victories over the insurgents .