Suspected militants have ambushed a military base in northeastern Nigeria, and killed as many as 30 soldiers.
The attack targeted a base in Zari village in the Guzamala local government area of Borno State on Thursday.
But details emerged later because the village is located in a remote area near the border with Niger.
"The battle lasted for about two hours and our colleagues fought them, but things became bad before the fighter jets arrived. We lost about 30 of our soldiers and about 10 were wounded," an unidentified military source confirmed on Saturday.
The violence, which has been attributed to a militant group identified as ISWA, undermines Nigeria's ongoing efforts to improve security and defeat militancy in the region, ahead of the upcoming presidential election.
ISWA is an offshoot of Boko Haram, the notorious group linked to the Takfiri terrorist group Daesh.
The Zari attack highlights the challenge to secure the northeast, months ahead of the February election in which security looks set to be a main issue.
President Muhammadu Buhari, a former general, who came to power in 2015 on a platform of stamping out rampant militancy, plans to seek a second term in office in the upcoming vote.
Militancy is still rife in the West African country despite the government's announcement in late 2015 that militants in the region had been largely defeated.
In July, Nigeria appointed the fourth commander in 14 months to lead the campaign against militancy.
Since 2009, the militants have killed 20,000 people and left over 2.6 million others homeless.