Gunmen seized the students just days after the separate kidnapping of around 280 children in the region, where criminal gangs target schools to extract ransom payments.

The army said it had freed 16 pupils and a woman on Thursday. The group were abducted in Sokoto state on March 9.

"The rescued hostages have been handed over to the Sokoto state government for further action," said spokesman Major General Edward Buba. He did not provide details on the operation.

At the time of the attack on an Islamic seminary in Gada district, staff told AFP the gunmen rounded up pupils as they slept outdoors. The woman was abducted in another part of the district.

The Sokoto kidnapping followed the mass abduction of about 280 pupils by a gang in Kuriga, Kaduna state, on March 7, which prompted a national outcry over insecurity.

Officials say troops have been searching forests to rescue the Kuriga students, but families say few details have emerged. Buba insisted "the military would not rest until all kidnapped hostages are rescued."

Kidnapping is rife in Nigeria and victims are often freed following negotiations with the authorities, though a 2022 law banned handing money to kidnappers.