Lagos: Gunmen have abducted 15 students and four staffers from a school in northwest Nigeria, police said Monday.
    
A police officer and two security guards were killed in the attack on the College of Agriculture and Animal Science in Zamfara state, police spokesman in the state, Mohammed Shehu, said in a statement on Monday.
    
The attack happened late Sunday, about a month after the school's provost was abducted and then released a few days later.
    
Zamfara is one of Nigeria's states attacked most by armed groups who often kidnap schoolchildren and travelers for ransom. In February this year, the bandits abducted 317 female students in an attack on another boarding school in Zamfara.
    
Since then, at least four mass school abductions in which a total of about 500 hostages, including children, have been reported in Nigeria's north, parts of which are still suffering attacks by Boko Haram extremists in their decade-long insurgency.
    
The abductors have released most of the students following efforts by Nigeria's security forces as well as negotiations. Authorities have expressed concern that the mediators could be working with Islamic extremists who remain active in Nigeria's northeast.