A group of UN rights experts have called on the United Arab Emirates to immediately free a leading human rights activist.

UN experts on Tuesday urged the UAE to release Ahmed Mansoor, a leading human rights activist, saying his arrest was a direct attack on the work of rights defenders.

Also, three independent experts with the UN human rights office in Geneva demanded information about the location of Ahmed Mansoor.

They said his secret detention in the UAE puts him at the risk of torture and ill-treatment.

Mansour, who was awarded the 2015 Laureate Martin Ennals Award for Human Rights Defenders, got arrested by police in Dubai on March 20. He was then transported to an unknown location.

Sources say that he was arrested shortly after signing a letter addressed to the Arab League summit, “calling to release prisoners of conscience and promote and protect human rights in the Arab world.”

He was previously placed under a travel ban by UAE authorities after being arrested for his work promoting human rights.

Human Rights Watch's Nicholas McGeehan has described the activist’s detention as “gut wrenching”, while the Emirates Centre for Human Rights accused the UAE of launching an assault on freedom of expression.