Nine Nigerian soldiers and a civilian have been killed during an operation to free 10 people abducted by militant Islam group Boko Haram, the army says.
The abducted group of geologists and surveyors were rescued during the battle, it added.
They were in a convoy that was ambushed as it was returning to north-eastern Maiduguri city on Tuesday.
At least 20,00 people have been killed and thousands more abducted since Boko Haram launched its insurgency in 2009.
In the most notorious abduction case, it seized 276 girls from a boarding school in the north-eastern town of Chibok in 2014.
It has since freed more than 100 of the girls, in exchange for the release of its fighters detained by Nigeria’s security forces.
The latest abductions have renewed fears about the threat posed by Boko Haram, and has caused widespread shock, reports the BBC‘s Naziru Mikailu from the capital, Abuja.
The abducted geologists and surveyors worked at the University of Maiduguri, and were highly respected in academic and social circles, he added.
The 10 were contracted by the state-run oil firm to work on oil exploration in the region when they were seized.