Updated

A group of U.N. experts is calling on the United Arab Emirates to immediately release a leading human rights advocate, saying his arrest was a "direct attack" on the work of rights defenders

Three independent experts with the U.N. human rights office in Geneva also on Tuesday demanded information about the whereabouts of Ahmed Mansoor, saying his secret detention in the UAE puts him at the risk of ill-treatment and torture.

They expressed concerns that Mansoor, who was arrested in a pre-dawn operation at his home March 20, was detained over his work with U.N. human rights mechanisms.

Mansoor received the prestigious Martin Ennals Award last year for bringing attention to arbitrary arrests, concerns of torture and issues around the independence of the judiciary in the UAE.