One million Nigerian children will likely stay away from school because of the threat of violence after a series of mass kidnappings and attacks targeting students this year, the UN said on Wednesday.

More than 1,000 pupils have been snatched in mass abductions for ransom by criminal gangs in Nigeria’s northwest and central states since December with dozens still in captivity.

The UN children’s agency UNICEF said there had been 20 attacks on schools in Nigeria this year and more than 1,400 pupils were taken and 16 had died.

Most have been released after ransom negotiations, but only after weeks or months in captivity, often in appalling conditions in rural camps.

“Families and communities remain fearful of sending children back to their classrooms due to the spate of school attacks and student abductions,” UNICEF said in a statement.

More than 37 million Nigerian children are due to start the new school year this month, the agency said, while an estimated one million would likely not return.

Some state governments have temporarily closed up schools after kidnappings.

Northwest and central states have long struggled with tit-for-tat violence between nomadic herder and farmer communities who battle over land and water.

Attacks escalated with the emergence of heavily armed criminal gangs, known locally as bandits, who raid villages, steal cattle and kidnap for ransom.

Bandit gangs this year have targeted schools and colleges in Nigeria’s northwest, snatching pupils and taking them into forest hideouts while they negotiate payments.

Around 70 students abducted nearly a fortnight ago were freed this we