An international rights group has urged Russia to release a Crimean Tatar leader Ilmi Umerov who has been sent to a psychiatric hospital.

Umerov, 59, is a former deputy chairman of Mejlis, the Crimean Tatars' representative body. He is also one of the most outspoken Tatar critics of the Kremlin and did not flee to mainland Ukraine following Russia's annexation of Crimea in 2014.

Crimea's Supreme Court effectively banned Mejlis in April.

Russia's Federal Security Service in May charged Umerov with separatism. Umerov earlier this month was taken to a mental asylum for a psychiatric evaluation even before a court could consider an appeal of that ruling.

Umerov's daughter and his lawyers say he has serious health issues and is not receiving proper medical care.