A column of Nigerian troops was attacked on Monday by fighters aligned to the Islamic State group outside the town of Marte in the Lake Chad region, the sources told AFP on condition of anonymity.
“We lost four soldiers and a vigilante,” said one.
The casualties were taken to a nearby base, a second source said.
Marte, which lies 130 kilometres (80 miles) from the regional capital Maiduguri, has been repeatedly targeted by the jihadists who attack military bases in the area.
The Nigerian army said its forces had thwarted an ambush by jihadists close to Marte after an “initial setback”, but did not give any death toll.
“The ambush was reinforced with a crudely prepared Improvised Explosive Device planted by them against the troops”, army spokesman Colonel Aminu Iliyasu said in the statement.
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The military said troops forced the fighters to “flee in disarray”, abandoning equipment including trucks, anti-aircraft guns, automatic rifles and ammunition.
Since July last year the Islamic State West Africa Province (ISWAP) group has intensified deadly attacks on military targets, raiding bases and ambushing troops.
ISWAP is a splinter faction of the Boko Haram jihadist group notorious for attacks on civilians.
The decade-long insurgency in northeast Nigeria has killed more than 35,000 people, displaced around two million and spilt over into neighbouring countries.
THE SUN, NIGERIA