Leading U.N. human rights experts are demanding that the United Arab Emirates immediately release five Libyans, including three with Canadian or U.S. dual citizenship, who allegedly have been subjected to waterboarding, electric shocks and lockups in a freezer over the last year and a half.

The call was timed with publication on Monday of an opinion by the U.N. Working Group on Arbitrary Detention, which late last year considered the cases of the five Libyans which have increasingly drawn the attention of advocacy groups like Amnesty International and Human Rights Watch.

The 13-page opinion cites allegations by advocates for the detainees that they have been deprived of sleep for up to 20 days; beaten on the hands and legs; and suffered "electric shocks with an electric chair." Some had been "hung with a rope around the neck" or had faced "constant death threats with guns being placed at the head."

"Some of them recounted being placed in a freezer for 45 minutes," the report said.

Neither a court nor a tribunal, the five-member working group can call countries and their leaders to account based on their own commitments to international conventions. As in the case of its recent opinion that WikiLeaks founder Julian Assange should be allowed to leave his sanctuary in the Ecuadorean embassy in London, it has no power of enforcement.

Dainius Puras, U.N. special rapporteur on the right to health, said in a statement that most of the detainees don't have adequate access to medical care and have faced health problems including loss of sight and hearing due to the alleged torture.

The working group findings identified the five as Adel Rajab Beleid Nasef; Moad Mohamed al-Hashmi; Salim Alaradi, who also has Canadian citizenship; and father and son Kamal Ahmed al-Darrat and Mohamed Kamal al-Darrat, who are also U.S. nationals. The report said it was not clear whether Nasef and Al Hashmi were still alive.

Alaradi was identified as a 48-year-old father of five and chief executive of a home appliance company who was arrested on Aug. 28, 2014 while on vacation in a Dubai hotel. At around midnight that day, the report said, Alaradi received a call asking him to come to the hotel, where he was met and detained by plain-clothes police officers.

The UAE government had no immediate comment on the report Monday. The experts said they had been in contact with Emirati authorities over the cases previously and found their reply "unpersuasive."

The Persian Gulf state has grown increasingly involved in the turmoil that has wracked Libya in recent months following the toppling of longtime leader Moammar Gadhafi in 2011.

The UAE was part of the NATO-led coalition that ousted Gadhafi and has taken a keen interest in the country's future since. It backs some members of the Libya's internationally recognized government.

The United States says the UAE carried out airstrikes in 2014 targeting Islamist militias in Libya, with Egypt providing logistical support. The Emirates has refused to comment on the allegations.

In November, authorities in Libya's militia-held capital, Tripoli, announced the arrest of an Emirati police officer on suspicion of being a spy, though Dubai police said the man in question was fired five years ago.