More than 40 people have died in north-east Nigeria during an attempt to free people who had been ambushed in a convoy by militant Islamist group Boko Haram, sources have told the BBC.
At least five members of an oil exploration team were killed and soldiers also died.
Army chiefs have now been ordered to relocate to the affected area.
The high number of casualties will be a blow for the government, which insists the insurgency is all but defeated.
At least 20,000 people have been killed and thousands more abducted since Boko Haram launched its insurgency in the city of Maiduguri, north-east Nigeria, in 2009.