Suspected members of Boko Haram have released a photograph that appears to show three kidnapped members of an oil exploration team in northeastern Nigeria, according to the university whose staff were part of the team and which distributed the image on Friday.The abduction of the oil survey team and a rescue attempt that led to multiple fatalities have led to a U-turn by the government and military, who earlier this month had said Boko Haram were defeated and all but eliminated. The defence minister told reporters on Thursday that the authorities were not in full control of the environment in the northeast at the moment, and that the military was trying to regain territory there.The team, which included university staff and employees from Nigeria's state oil firm, was kidnapped by suspected militants from Islamist insurgency Boko Haram while searching for oil in the conflict-ridden northeast on Tuesday. A rescue attempt on Wednesday ended in the deaths of at least 37 members of the original prospecting team and the rescuers, including Nigerian military and armed vigilantes.Friday's photograph, released by the University of Maiduguri, appears to shows three of its staff, seemingly unharmed, sitting crosslegged on a red floor in front of a patterned wall. The university gave the names of the staff pictured, but declined to give any further details. Four staff members are missing in total, a university spokesperson said. Also on Thursday, Acting President Yemi Osinbajo dispatched the chiefs of the military to the northeast to help regain control of the situation.Of those killed in the kidnapping and attempted rescue, five are staff from the University of Maiduguri, 22 are from the vigilante Civilian Joint Task Force and 10 are military, according to officials and military sources. Northeastern Nigeria has been wracked for eight years by an Islamist insurgency that has killed at least 20,000 people and forced some 2.7 million to flee their homes.The Nigerian National Petroleum Corporation, which contracted university staff, has for more than a year surveyed what it says may be vast oil reserves in the Lake Chad Basin. It is aiming to reduce its reliance on the southern Niger Delta energy hub, which last year was hit by militant attacks on oil facilities. The government and military have repeatedly said Boko Haram is on the verge of defeat. In December, President Muhammadu Buhari said the group's last stronghold, an enclave in the Sambisa forest, had fallen. But insurgents have launched attacks with renewed zeal in the past few months.The latest attack brings the death toll in Maiduguri and its environs since early June to at least 99. Seventeen people were killed in the city in one week alone this month.