United Nations human rights experts have formally condemned the punishment of a Tibetan education advocate who was sentenced to five years in prison after giving interviews to The New York Times.

Since his detention in January 2016, the advocate, Tashi Wangchuk, 33, has become one of the most prominent symbols among critics of China’s legal system and policies in Tibetan regions. In sentencing him on May 22, a court said he was guilty of “inciting separatism.”

On Wednesday, six United Nations experts issued a statement from Geneva.

“We are gravely concerned,” they said, “about the sentencing of Mr. Tashi Wangchuk, and the sanctioning of his right to freely express his opinion about the human rights of the Tibetan minority of China.”

The experts expressed regret that the court sentenced Mr. Tashi despite their having twice called on China to drop the charges and release him immediately.