Norwegian Prime Minister Erna Solberg said there was no reason to doubt the claim, and called it a "barbaric act".
The Chinese foreign ministry also said it was shocked by the killings.
IS Dabiq magazine published what it said were photographs of the men, alive and dead. They appeared to have been shot.
Ms Solberg said: "There are no excuses for the treatment our countryman has been subjected to, it can`t be found in religion, nor ideology."
"This is a despicable and barbaric act," she added.
Chinese foreign ministry spokesman Hong Lei said in a statement China has noted the report and is "deeply shocked".
"Ever since the Chinese citizen was held hostage by the Islamic State group, the Chinese government has been sparing no effort in rescuing him," Mr Hong said. "We are still verifying the information."
The militants announced the two men`s capture in a previous issue of Dabiq, which showed them in yellow jumpsuits, but gave no detail about their capture.
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