At least eight Nigerian soldiers were killed and 50 wounded when Islamist Boko Haram insurgents attacked a military formation in Borno State, security sources said on Wednesday.
The militants arrived by motorcycle and in armoured vehicles in the incident on Monday, the sources said.
A military source said the military formation was part of an offensive to flush out insurgents from the Timbuktu Triangle, a longstanding militant stronghold in northeastern Nigeria.
The insurgents engaged the troops in a heavy gun battle, according to the sources.
In a statement on Wednesday, the military said troops had cleared several Islamist strongholds in the Timbuktu Triangle and disrupted planned attacks with vehicle-borne improvised explosive devices (VBIEDs).
The military said troops neutralised one explosive-laden vehicle, but a second breached defensive positions, killing several soldiers and members of the Civilian Joint Task Force, a civilian militia that supports the military.
A CJTF member confirmed the attack and said government forces had been outnumbered during the assault.
The Timbuktu Triangle, a vast and difficult-to-access area spanning parts of Borno State, has for more than a decade served as a base for Boko Haram fighters launching coordinated attacks on military positions and civilian communities.
Boko Haram, a jihadist group that emerged in northeastern Nigeria in 2009, has killed tens of thousands of people and displaced millions across Nigeria and neighbouring countries.
The group has since split, with one faction aligning with Islamic State to form Islamic State West Africa Province (ISWAP), which has increasingly targeted military bases in recent years.
Despite repeated military offensives, Boko Haram and its splinter groups have continued to mount large-scale attacks, exploiting difficult terrain, porous regional borders, and a limited state presence in parts of the arid northeast.
The Nigerian military has since withdrawn its forces from the triangle to a base in Damboa, according to the sources. The bodies of those killed and the wounded were being transported to the military hospital at Maimalari Barracks in Maiduguri.
