A United Nations rights panel has issued a strongly worded opinion calling on Iran to immediately release an American scholar imprisoned two years ago while doing historical research that the Iranian authorities had approved.

The opinion, by the United Nations Working Group on Arbitrary Detention, said the scholar, Xiyue Wang, a graduate student at Princeton University, had been wrongly accused of espionage, secretly tried and imprisoned.

“The Working Group requests the Government of the Islamic Republic of Iran to take the steps necessary to remedy the situation of Mr. Wang without delay and bring it into conformity with the relevant international norms,” stated the opinion, dated Aug. 23.

The United Nations has not publicly released the opinion but Princeton University posted a summary of the findings on its website, along with a plea from Princeton officials and Mr. Wang’s wife for his release.