LAGOS, Nigeria (AP) — Gunmen have abducted 73 students in a new school attack in northwestern Nigeria on Wednesday, police said, just days after three other groups of hostages were freed when large ransom payments were reportedly made.

Attackers descended upon the Government Day Secondary School located in the remote village of Kaya, according to Zamfara state police spokesman Mohammed Shehu. A rescue operation was ongoing to free the students, he added.

More than 1,000 students have been kidnapped from schools in northern Nigeria since December. The gunmen have demanded large ransom payments from parents, and while most pupils ultimately have been released, some have died or been killed in captivity.