Suspected Islamist fighters launched a coordinated attack on an army base and a military outpost in Borno State, killing at least 16 people, security sources told Reuters.
Boko Haram and Islamic State West Africa Province militants have mainly operated in the northeast of Nigeria, attacking security forces and civilians and killing and displacing tens of thousands of people.
In the latest assault, Boko Haram insurgents and ISWAP fighters struck an army base in the Wajiroko area of Borno State at about 2100 GMT on Monday and set military equipment on fire, the sources said.
One of the soldiers in the Wajiroko brigade said at least four soldiers had been killed and several others injured, including the brigade commander.
Armed fighters in light tactical vehicles also stormed an outpost in Wulgo, a village about 12 kilometres (7.5 miles) from the Cameroonian border town of Fotokol, killing 12 soldiers and injuring a dozen others, Cameroon's Defence Ministry said on Wednesday.
A military source who asked not to be named told Reuters the raid that targeted soldiers who are fighting the insurgency as part of a multinational task force took place between midnight and 3 a.m. local time on Tuesday.
The source added the militants were suspected to have initially launched their attack using drones before advancing with a ground assault. "They looted an important stockpile of weapons," the source said.
Videos shared on social media showed bloodied bodies lying on the ground after the attack, charred patrol vehicles and damaged buildings. Reuters could not independently verify those videos.
A Nigerian army spokesperson did not respond to requests for comment. Cameroon army spokesperson Cyrille Serge Atonfack Guemo confirmed the attack but said the casualty figures were still unclear.
Makinta Modu, a member of a local militia recruited to help the Nigerian army, said in the Wajiroko attack militants overran an army "forward operation base".
"Around 10:30 p.m. (2130 GMT) air force fighter jets came for reinforcement ... and killed many of the ISWAP fighters that captured the military base," Modu said. It was not clear whether the army had regained control over the base.
Although weakened by military assaults and internal fighting over the years, Boko Haram and ISWAP have stepped up attacks on military and civilian targets in Borno this year.
An Islamist insurgency has plagued the northeast of Africa's most populous country for more than a decade, while kidnapping and banditry are rampant in the northwest and gang and separatist violence is common in the southeast.
Reuters
