Rescue operation was carried out by the military after Boko Haram militants abducted members of a team searching for oil in Nigeria's northeast.
At least 50 people including civilians and members of the military have died after an attempted rescue of an oil exploration team kidnapped by suspected Boko Haram militants in northeast Nigeria, officials said on Thursday.
The team searching for oil in Nigeria's conflict-ridden northeast was made up of members from the state oil firm and university researchers and staff, while the attempted rescue was carried out by military personnel and vigilantes.
The military said a day earlier that it had recovered the bodies of nine soldiers and a civilian during its rescue of staff from the Nigerian National Petroleum Corporation (NNPC) who were on the survey team.
The total number of military personnel killed was 12, said one military source in Nigeria's northeast, who declined to be identified because the source was not authorised to speak to media.
The military's statement on Wednesday did not refer to team members from the University of Maiduguri, which contributed staff including geologists to the team surveying in the Lake Chad Basin region.
A spokesman at the university, Deputy Director of Information Ahmed Mohammed, said on Thursday two university academics and at least one driver were among at least five dead.
Four others staff members from the university are missing, he said.
Sixteen members of the Civilian Joint Task Force (CJTF) were also killed, Bunu Bakar, secretary of the armed vigilante group, said.
Nigeria's oil minister said he was awaiting official confirmation from military authorities on the kidnapping and attempted rescue of people including NNPC staff, declining to comment on the death toll.
A military spokesman did not reply to phone calls and text messages requesting comment.
Spike in attacks
Nigerian Minister of Defence Mansur Ali blamed the summer wet season for the spike in attacks in the northeast and the loss of control of territory that the army clawed back from Boko Haram last year.
"We cannot dominate the environment like what we do during the dry season, but effort is geared towards regaining back our areas," he told reporters in Abuja after an emergency meeting with Nigeria's acting president and military chiefs.
Northeastern Nigeria has been wracked for eight years by an insurgency that has killed at least 20,000 people and forced some 2.7 million to flee their homes.
The NNPC, 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.
Nigeria's 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 brought the death toll in Maiduguri and its environs since early June to at least 92. Seventeen people were killed in the city in one week this month.