At least 17 soldiers were killed in northern Nigeria when gunmen stormed three army bases, security sources and a local official said on Wednesday, the latest assault in a region plagued by violence.

Armed gangs operating in the northwest, known locally as bandits, typically engage in kidnapping for ransom and target security forces.

The Nigerian Army confirmed the attacks on Tuesday but did not provide details.

“Sadly, some gallant warriors paid the supreme price in the day-long battles while four troops wounded in action are currently receiving treatment for their gunshot wounds,” the army said in a statement.

Two security sources said gunmen launched surprise attacks on the army’s forward operating bases in the Kwanar Dutse Mariga and Boka areas in Niger State and another base in neighbouring Kaduna State, battling troops for several hours.

The sources and Abbas Kasuwar Garba, chairman for Mariga district, said all 17 fatalities were at the Kwanar Dutse Mariga base.

“It was an ambush. They (gunmen) came from nowhere and used heavy ammunition to attack,” said a Niger-based army officer.

The Nigerian Army said it launched counterattacks, killing several gunmen.

Insecurity has stretched Nigeria’s military, as it confronts armed gangs alongside Islamist groups Boko Haram and an Islamic State affiliate in the northeast.

Niger State has witnessed ambushes against military personnel, with Boko Haram fighters known to operate there.