MADRID (AP) — The United Nations Working Group on Arbitrary Detention has asked Spain to seek the release from pre-trial jail of three Catalan separatists detained following Catalonia's 2017 secession attempt.

In an opinion to be published later Wednesday but seen by The Associated Press, the working group says that former Catalan regional vice president, Oriol Junqueras, lawmaker Jordi Sànchez and activist Jordi Cuixart were arbitrarily detained and their rights violated.

The three, who are considered a flight risk by Spanish authorities, are among a dozen separatist leaders on trial at Spain's Supreme Court on a number of charges, including rebellion.

The working group is made up of five independent, non-paid experts appointed by the Human Rights Council. The opinion matters for those countries mindful of international commitments.