An overnight explosion at the US embassy in Oslo may have been an act of terrorism, Norway's police have said. The embassy in the Norwegian capital sustained minor damage after the blast in the early hours of Sunday - but no-one was injured. "One of the hypotheses is that it is an act of terrorism, but we are not completely locked into it," Frode Larsen, the head of police joint investigation and intelligence unit, told Norway's public broadcaster NRK. Norwegian authorities say they are in contact with US diplomats, and an investigation into the incident is now under way. A US State Department spokesperson said they are "aware of an incident at the US Embassy in Oslo" and are investigating. Speaking to NRK later on Sunday, Larsen stressed that "we have to be open to the possibility that there may be other causes behind what has happened". In an earlier statement, Norway's police said that "large resources" were sent to the area around the US embassy at about 01:00 local time on Sunday (00:00 GMT).…