At least 200 gunmen were killed in the past three days in Nigeria's central-northern state of Niger during a security operation to clear armed gangs from the area, a state commissioner said on Thursday.

Gunmen have terrorised citizens in the north and northwest of the country and have gained notoriety for kidnapping hundreds of students and villagers for ransom and killing dozens.

The Niger regional commissioner in charge of internal security, Emmanuel Umar, said some leaders of the armed gangs, known locally as bandits, were among those killed during an operation led by the army and volunteers from local vigilante groups and community leaders.

In a statement, Umar said 60 motorbikes, which the gangs use to raid villages, weapons and cattle, were recovered from gunmen operating from camps deep inside the vast forests in the state.

An army spokesman did not immediately respond to questions.

At least four Nigerian security personnel were killed when their patrol vehicle detonated a landmine in Niger last month, and gunmen killed an unknown number of people.

Niger regional authorities said last year that Islamist militants had established a presence in one locality for the first time. Last month, President Muhammadu Buhari said the military had begun a major offensive against militants there.

Reuters