A nuclear research reactor in Norway had to be shut down after an alarm signal sounded, the Norwegian Radiation Protection Authority (NRPA) announced.
In a statement, the agency said no radiation leak had been detected around the building housing the reactor at a technical institute in Kjeller, some 25 kilometers (15 miles) from Oslo.
The incident occurred at 3:00 am (0100 GMT) when an alarm was triggered, setting in motion safety procedures.
"The situation is under control, (the reactor) is shut down and all the emergency measures have been taken," Ingar Amundsen, an adviser at the NRPA, told AFP.
"Elevated levels of radioactivity" were detected "in (the) primary circuit" of the reactor, Amundsen said, but confirmed there was "no leakage" outside the building.
No one was in the building when the alarm sounded and no residents were evacuated from the surrounding area.
Another spokeswoman for the radiation authority, Alte Valseth, was quoted by the NTB news agency as saying that increased levels of radiation were detected in water used to cool the reactor and also in the air surrounding it.
Samples from water in the reactor have been taken for analysis and test results were expected later in the day, Valseth said.
Norway has no nuclear power plants, but two small research reactors used for medical research.
Amundsen said the cause of the incident was so far unknown, but that it might have been due to a leak in a nuclear fuel rod.
"It is a serious matter but there was no risk that nature or people would be affected," the authority's director, Per Strand, added in a statement. "The safety system functioned as it should have."