This was a scheduled flight from Oslo Airport Gardermoen (ENGM) to Bardufoss Airport (ENDU). The crew ordered de-icing. ”WING ANTI ICE” was used during taxiing. Following the de-icing routine, and take-off from runway 19L Gardermoen, once the fog was cleared, the wings were inspected. The crew discovered that there was ice both on the leading edge and the upper surface of both wings. The ice could not be removed using “Wing Anti Ice”. The arrival location, Bardufoss, was experiencing icing conditions. For this reason, the commander decided to carry out an unscheduled landing at Trondheim Airport Værnes (ENVA) to remove the ice. The weather conditions there were fine with above-zero temperatures. During approach the ice melted. No technical faults were discovered. The flight then continued to its destination.