A 17-year-old has died after explosives he appears to have been trying to make in his Oslo flat detonated.
The blast blew out some windows in the block and left the victim's 19-year-old brother injured. Three other friends escaped unhurt.
Norwegian police said internet instructions on how to make explosives and some powder were found at the flat.
Police are questioning those present but are not reported to think they had links to any extremist groups.
Other apartments in the three-storey block were evacuated after the blast.
"At the scene we found written instructions on how to make explosives and some powder that the youngsters had mixed," Inspector Vidar Hjulstad told Norwegian public radio NRK.
The powder has been sent for analysis.