Roughly 60,000 liters of oil leaked at a transformer station near Oslo on Sunday after the premises were reportedly broken into.
On Monday, Norwegian police said they were investigating the break-in at the disused electricity transformer station in Norway's Bærum municipality.
Part of the fence surrounding the premises had been cut and the cover at the bottom of the transformer was unscrewed and left open. National power grid operator Statnett believe the incident was an act of deliberate sabotage.
"It appears that someone has broken in and removed a cover on the transformer, and left it open, causing a significant amount of oil to spill out," Thomas Fennefoss, Project Manager at Statnett said.
However, police authorities said in a statement that they currently had no concrete evidence to confirm so.
The oil, harmful to the environment but not to humans, reached the Sandvikselva River nearby the station. Some of the oil also seeped underground.
Richard Kongsteien, Communication Manager for Bærum municipality, said efforts are underway to minimise the environment impact. Oil barriers and absorbents have been deployed to contain and clean up the spill.
