FILE PHOTO: People hold banners depicting Catalan leaders' faces as they gather ahead of a rally of Catalan separatist organisations, in Madrid, Spain March 16, 2019. REUTERS/Juan Medina/File Photo

BARCELONA (Reuters) - Spain must release three jailed Catalan separatist leaders denied bail while facing trial for their role in the region’s failed bid for independence in 2017, a United Nations expert group will say in a report on Wednesday.

In an advance copy seen by Reuters, the U.N. Working Group on Arbitrary Detention said Spain should investigate the “arbitrary” decision to deny bail to Oriol Junqueras, Jordi Sanchez and Jordi Cruixart and give them a chance to seek compensation.

Nine former Catalan leaders are in jail while standing trial on charges including rebellion and misuse of public funds related to their alleged role in organizing a 2017 referendum on secession and subsequent declaration of independence.

The report comes a day after the European Court of Human Rights (ECHR) unanimously rejected a case brought by dozens of Catalan politicians alleging Spain’s constitutional court violated their rights by blocking a session in the regional parliament at the height of the secession crisis.

The U.N. Working Group does not have the authority to order the release of a detainee, depending instead on moral weight to put pressure on governments, although ultimately its rulings have often been ignored in the past.

Catalan regional president Quim Torra, speaking in a televised address on Wednesday, said that in light of the report he would issue a formal request to Spain’s public prosecutor to release and drop all charges against those on trial.

But a senior Spanish government source told Reuters the report was flawed. “The report by the Working Group on Arbitrary Detention raises doubts about its independence and impartiality,” the source said.