Updated

Officials say a small fire broke out in Sweden's Ringhals nuclear power plant earlier this week as workers carried out maintenance on a reactor containment unit.

The unit, which contains one of Ringhals' four reactors, had been shut down for maintenance since April 2 and all radio active material had been moved to another building, said Officials. Radiation levels within the unit were not heightened by the incident and no one was injured.

Ringhals spokesman Gosta Larsen said Thursday the small blaze, detected through a small temperature rise inside the containment, broke out amid a pressure test at around midnight between Tuesday and Wednesday.

It is not clear what caused the near 20 minute long fire and the test has been suspended while the incident is being investigated.