Gunmen kidnapped 140 students from a boarding school in northwestern Nigeria on Monday, a school official said, the latest in a wave of mass abductions targeting schoolchildren and students.

Heavily-armed criminal gangs often attack villages to loot, steal cattle and abduct for ransom in northwest and central Nigeria, but since the start of the year they have increasingly targeted schools and colleges.

The attackers opened fire and overpowered security guards after storming the Bethel Baptist High School in Kaduna state in the early hours of Monday, abducting most of the 165 pupils boarding there overnight.

“The kidnappers took away 140 students, only 25 students escaped. We still have no idea where the students were taken,” Emmanuel Paul, a teacher at the school told AFP.

Kaduna state police spokesman Muhammed Jalige confirmed the early Monday morning attack, but could not give details on the number of pupils taken.

“Tactical police teams went after the kidnappers,” he said. “We are still on the rescue mission.” Police said they had safely rescued 26 people, including a female teacher.

Around 1,000 students and pupils have been abducted in Nigeria since December. Most have been released after negotiations with local officials, although some are still being held.

Often, gangs target rural schools and colleges where students stay in dormitories and security is light, allowing them to easily transport large numbers of victims to forest hideouts to negotiate ransoms.

Forest hideouts

The kidnapping of Nigeria schoolchildren first made international headlines in 2014 when jihadist group Boko Haram snatched nearly 300 schoolgirls from a rural school in Chibok in northeast Borno state.

Recent abductions by gunmen have prompted six northern states to shut public schools to prevent such attacks.

Bethel Baptist High School is a co-education college established by the Baptist church in 1991 at Maramara village in Chikun district outside the state capital Kaduna.

Monday's attack was the fourth mass school kidnapping in Kaduna state since December.

Kaduna state governor Nasir Ahmad El-Rufai has been one of the most vocal local leaders insisting he will refuse to pay ransom money.

Monday's school abduction came just hours after gunmen snatched eight medical employees from a Kaduna health centre, according to police.

President Muhammadu Buhari, a former general first elected in 2015, has promised to end the scourge of kidnapping and criminal gangs, but the mass abductions are only one challenge facing his government.

Nigeria's security forces have been battling a jihadist insurgency the northeast since 2009, a conflict that has killed around 40,000 people and displaced more than two million more.

The criminal gangs, known locally as bandits, operate from camps in the vast Rugu forest, which cuts across Zamfara, Katsina, and Kaduna states in Nigeria, as well as neighbouring Niger.

Nigeria's air force has in the past attacked bandit camps while some northern states have sought to negotiate with the gangs by offering amnesties in return for disarmament.

But attempted ceasefires have failed and local negotiations have been mostly opposed by Buhari's government which has warned that rewarding bandits would backfire.