The explosions are both believed to be hand grenades (Picture: EPA)A boy, 13, has been arrested after a ‘grenade’ exploded in Oslo, Norway. The blast is believed to have been caused by a hand grenade, operations manager Øyvind Hammervold said. Police then detonated a second unexploded, ‘military-style’ hand grenade at around 9.44pm. ‘A car wanted to drive on, but then the man stood in front and stopped the car again. Photographs from the scene show an unexploded hand grenade can be seen in the middle of a pedestrian crossing.