Oslo - Norwegian police officers Thursday staged a nationwide strike in protest against changes in regulations for working hours.

The 90-minute strike was called by the Norwegian Police Federation.

Union leaders said they were angered that they were not allowed to take part in negotiations concerning changes to working hours, and that police officers were forced to have shorter time off periods posing a possible threat to their health.

In the west coast city of Bergen, police officers called for Justice Minister Knut Storberget to resign, local media reported.

During the protest that ended at 12.30 pm (1130 GMT), police stations were reduced to skeleton staffing. Switchboards were staffed to ensure responses to emergencies.

The Norwegian Police Federation has some 11,700 members including police officers and civilian police force employees. (dpa)