GENEVA (AP) — U.N. human rights experts say Russia violated international law by imprisoning Wall Street Journal reporter Evan Gershkovich and should release him “immediately.”

The Working Group on Arbitrary Detention, made up of independent experts convened by the U.N.’s top human rights body, said there was a “striking lack of any factual or legal substantiation” for spying charges leveled against Gershkovich, 32.

The five-member group said Gershkovich’s U.S. nationality has been a factor in his detention, and as a result the case against him was “discriminatory.”

Matthew Gillett, the working group’s chair, said its opinion was grounded in the International Covenant on Civil and Political Rights, which was adopted in 1966 and nearly all U.N. member countries have ratified.

“The covenant is something that Russia has freely signed up to and accepted the obligations under, and therefore as a matter of international law, it is obliged to implement the provisions of the covenant,” he said in an interview.

Gillett said Russia should provide Gershkovich “proper reparations” for holding him for over a year in detention without a legitimate basis.

Gershkovich went on trial behind closed doors on Wednesday in the Russian city Yekaterinburg, where he was arrested on March 29 last year while on a reporting trip on espionage charges that he, his employer and the U.S. government vehemently deny.

The U.N. group said in its findings that because the detention of Gershkovich was arbitrary, no trial should take place. The group cannot compel any response from Russia, and is mandated to look into cases in which countries violate international commitments that they make.

"Taking into account all the circumstances of the case, the appropriate remedy would be to release Mr. Gershkovich immediately and accord him an enforceable right to compensation and other reparations, in accordance with international law," the UN group said.

Almar Latour, the publisher of the Wall Street Journal, commended the U.N. panel and said: “Evan’s wrongful detention is a flagrant violation of his fundamental human rights."

“As the U.N. working group recognizes, Russia is violating international law by imprisoning Evan for his journalism, silencing critical reporting, and depriving him of due process and other rights,” Latour said, calling on the U.S. and world leaders "to do everything they can to bring Evan home now.”

Gershkovich, the U.S.-born son of immigrants from the USSR, is the first Western journalist arrested on espionage charges in post-Soviet Russia. Russian authorities, without presenting evidence, claimed he was gathering secret information for the United States.

He faces up to 20 years in prison if convicted, which is almost a certainty since Russian courts convict more than 99% of the defendants who come before them.

The State Department has declared Gershkovich “wrongfully detained,” thereby committing the government to assertively seek his release.

Russia has signaled the possibility of a prisoner swap involving Gershkovich, but it says a verdict — which could take months — would have to come first.