LAGOS, Nigeria (AP) — Rebels from the Boko Haram extremist group claimed responsibility Tuesday for abducting hundreds of boys from a school in Nigeria’s northern Katsina State last week in one of the largest such attacks in years, raising fears of a growing wave of violence in the region.

More than 330 students remain missing from the Government Science Secondary School in Kankara after gunmen with assault rifles attacked their school Friday night, although scores of others managed to escape.

The government and the attackers are negotiating the fate of the boys, according to Garba Shehu, a spokesman for Nigerian President Muhammadu Buhari.

“The kidnappers had made contact and discussions were already on, pertaining to the safety and return” of the children to their homes, said Shehu on Twitter during talks with Katsina Governor Aminu Masari. Neither official said whether the negotiations are with Boko Haram or another group.

Masari said security agencies “deployed for rescue operations have also informed us that they have located their position.”

The Daily Nigerian said it received an audio message from Boko Haram leader Abubakar Shekau claiming the abduction, although there has been no independent verification of its authenticity.

The Islamic extremist group has carried out mass abduction of students before. The most serious took place in April 2014, when more than 270 schoolgirls were taken from their dormitory at the Government Secondary School in Chibok in northeastern Borno State. About 100 of the girls are still missing.

In February 2014, 59 boys were killed during a Boko Haram attack on the Federal Government College Buni Yadi in Yobe State.

In the audio message about Friday’s attack, Shekau said his group abducted the schoolboys because Western education is against the tenets of Islam.

More than 600 students attend the school. Many were able to escape during a gunfight between the attackers and the police, according to state police spokesman Gambo Isah.

Students corroborated this account with various news agencies, saying many of them were also rounded up and forced to walk to a nearby forest, where some were also able to flee.

Several armed groups operate in northern Nigeria, where Katsina State is located. It was originally believed that the attackers were bandits, who sometimes work with Boko Haram.

Bandits have operated in the northwest region for some time, and kidnappings have increased in recent years. Amnesty International says that more than 1,100 people were killed in the first six months of 2020 in violence related to attacks by bandits.

A joint rescue operation was launched Saturday by Nigeria’s police, air force and army after the military engaged in gunfights with bandits after locating their hideout in the Zango/Paula forest.

If Boko Haram is proven to be behind the abduction, it could mean a new wave of religious extremism is on the rise in Nigeria. For more than 10 years, the group has engaged in a bloody campaign for introducing strict Islamic rule, but it has been mainly active in northeast Nigeria, not in the northwest, where Katsina State is located. Thousands have been killed and more than a million people displaced by the violence.

Nnamdi Obasi of the International Crisis Group said a shift of Boko Haram’s activities to the northwest would have serious security implications because it could partner with other armed criminal groups known to carry out attacks and collect payments from households and markets.

“They are Iike mini-armies that are able to carry out operations in defiance of the security forces, and it is worrisome,” Obasi told The Associated Press.

The local armed groups have no religious ideology, however, and Obasi said Boko Haram’s movement into the northwest would create “a risk of convergence between criminal groups and jihadist groups. The trajectories are very disturbing.”

Because the northwest is more homogeneously Islam than the northeast, there are more potential recruits for radicalism.

Friday’s abduction has become a rallying cry for Nigerians fed up with growing violence, with #BringBackOurBoys trending on Twitter as people express their frustrations. A similar #BringBackOurGirls became an international rallying cry for the Chibok girls.

“Before now, it has been bandits and kidnappers terrorizing our state, but little has been done to address the situation,” said Mallam Saidu Funtua, a member of a local civil society organization in Katsina State.

He added that “the abduction of students was the height of it all. It is unacceptable and the government has to do more” to protect students and residents.

The attack was a major setback for education in Katsina, which was beginning to make progress in enrolment, he said, adding: “Our people will be discouraged in sending their kids to school.”

Kankara villager Lawal Muhammed said the attack left most residents terrified and traumatized.

“We have never experienced this kind of thing before,” he said. “We want the government to do more in protecting our children, especially now that schools would be resuming after the COVID-19 break.”

The abductions also come as Boko Haram and the Nigerian military may be investigated for war crimes in the rebels’ insurgency, which has lasted more than a decade.

The International Criminal Court’s chief prosecutor last week said a probe has found enough evidence to merit opening a full-scale inquiry into allegations of war crimes and crimes against humanity by Boko Haram extremists as well as into charges that Nigerian government forces have also perpetrated abuses.

Prosecutor Fatou Bensouda said there is a “reasonable basis to believe” Boko Haram and splinter groups linked to it committed crimes including murder, rape, sexual slavery and torture, as well as intentionally targeting schools and places of worship and using child soldiers. While a vast majority of the criminality in the conflict has been carried out by Boko Haram, prosecutors also found grounds to believe members of Nigeria’s security forces had committed crimes, she said.

Amnesty International last week released a report saying at least 10,000 civilians have died in Nigerian military custody since 2011 after being detained in connection with the Boko Haram insurgency in northern Nigeria.