After dozens of children were kidnapped by gunmen in Nigeria’s northern Zamfara State on Wednesday, schools in the state were forced to close.

In Zamfara’s Maradun area, at least 73 pupils were taken from a state-run high school, according to local police, who added that the high school was targeted by “armed bandits.”

“The abduction followed the invasion of the school by a large number of armed bandits,” authorities said.

Zamfara State Police Command said they have now formed a search and rescue team to work with the military to locate the abducted children. Officials said they have also deployed additional personnel to increase the security at Kaya village and neighboring areas to dissuade any further attacks.

“We have closed primary and secondary schools in the state but schools currently writing examinations are asked to stay behind until they finish their examinations,” Zamfara’s Information Commissioner, Ibrahim Dosara, said.

The kidnapping occurred only days after 91 pupils that were seized in north-central Niger State were freed by their kidnappers after their families paid a ransom of thousands of dollars.

Kidnapping for ransom has become one of Nigeria’s most serious security issues, with multiple mass kidnappings in Zamfara and other surrounding northern regions this year.

The kidnapping of nearly 200 schoolgirls in the town of Jangebe in February marked a high point in Zamfara’s run of kidnappings. The students have subsequently been released, and police have said that no ransom was paid in exchange for their release.

According to research published last year by Lagos-based SBM Intelligence titled “The economics of the abduction business in Nigeria,” an estimated $18.34 million in ransoms were paid between June 2011 and the end of March 2020.