Gunmen have abducted six girls and two staff members from a boarding school in northern Nigeria, according to a police spokesperson. Yakubu Sabo said armed men gained entry on Thursday into the Engravers College, a mixed boarding school in a remote area south of the city of Kaduna. They "took away two staff of the college and six female students to an unknown destination", Sabo said. It was not immediately clear who had taken them."The Kaduna state police command has mobilised and dispatched some operatives with a view to trail the perpetrators of this crime and rescue the victims and apprehend the criminals. The operation is still ongoing," he told Al Jazeera by phone. An official at the school confirmed the kidnapping to AFP news agency."Unknown gunmen broke into the school around 00:10 (23:10 GMT) and took away six female students and two staff who live inside the school," Elvis Allah-Yaro said. Abductions for ransom are common in Nigeria and the highway from the capital Abuja to the city of Kaduna has seen a surge in attacks by armed criminals, but raids on schools are rare. In 2014, the armed group Boko Haram abducted 276 schoolgirls from the remote northeastern town of Chibok in the Borno state.About 100 of those schoolgirls remain missing.Last week, police in the city of Kaduna freed hundreds of men and boys from a purported religious school where they had been beaten and abused.