Dozens of people were killed in a Boko Haram attack on an oil exploration team in northeast Nigeria earlier this week, military, medical and humanitarian sources told AFP.

"The death toll keeps mounting," said one source involved in dealing with the aftermath of Tuesday's attack near Magumeri, adding: "Now we have more than 50 and ... more bodies are coming in."

Others said the death toll was "at least 30".

Details of the ambush, which was initially thought to be a kidnapping attempt, have been slow to emerge, as the military strictly controls access to Borno state, which has been at the centre of Boko Haram violence.

Telecommunications and other infrastructure have been severely damaged or destroyed in the conflict, which has left at least 20,000 dead and more than 2.6 million homeless since 2009. 

The military said on Wednesday that ten people were killed in the attack, which targeted a team from the Nigerian National Petroleum Corporation (NNPC) and geologists from the University of Maiduguri.

But an aid agency worker in Magumeri, which is 50km northwest of the Borno state capital, Maiduguri, said "47 bodies were recovered from the bushes around Magumeri" by Wednesday morning.