A car containing an "extremely significant" bomb has been intercepted in the Republic of Ireland as it was being driven across the border for an attack in Northern Ireland, gardaí (Irish police) have said. The vehicle was stopped in County Monaghan on Wednesday during an operation targeting dissident republican activities. BBC News NI understands police in Northern Ireland's main theory is that the bomb was set to be used to attack a police station north of the border. Police sources in Northern Ireland believe the New IRA was likely responsible. Irish broadcaster RTÉ reported that gardaí sources said the bomb contained a power unit, a detonator and military grade explosives.