ISIL had two months ago demanded a ransom for the release of the men.
The announcement came in the latest issue of the group's English-language magazine on Wednesday, which contained a page that appeared to show the bodies of the two captives.
The group had earlier identified the Norwegian man as Ole Johan Grimsgaard-Ofstad, 48, from Oslo, and the Chinese man as Fan Jinghui, 50, a freelance consultant from Beijing.