United Nations rights experts urged Bahrain Wednesday to free Shiite opposition leader Sheikh Ali Salman, on trial for allegedly trying to overthrow the country’s Sunni regime.

Salman, 49, was arrested December 28, shortly after he was re-elected head of Bahrain’s main opposition party Al Wefaq.

He was charged with trying to incite regime change by non-peaceful means, and was denied bail when his trial opened last week.

“The charges appear to stem from the government’s dissatisfaction with opinions that Sheikh Salman expressed in public speeches and televised interviews, in which he called for the establishment of a democratic regime and for government accountability,” the five UN experts said in a statement.

“If this is indeed the case, his arrest and prosecution would amount to a breach of his fundamental human rights to freedom of expression, freedom of association and freedom of religion or belief,” they said, demanding that the government “clarify the situation.”

The UN’s top experts on those freedoms and on arbitrary detention and the situation of human rights defenders also cautioned that Salman may not be getting a fair trial, pointing out that his lawyer was “allegedly not allowed to examine the evidence to prepare for his defence.”

Salman’s arrest has sparked near-daily protests across the Shiite-majority but Sunni-ruled kingdom.

“Particularly worrying are recent reports that indicate that peaceful demonstrations following his arrest were disbanded by the authorities, including through the use of force,” the experts said, noting reports that at least 150 people had been arrested and some 90 injured during the demonstrations and in clashes with the police.

“We urge the government of Bahrain to promptly release all those who have been detained for peaceful expression of their views,” the UN experts said.

They also criticised Bahrain for revoking the citizenship of 72 people, in a move they described as “yet another attempt by the government of Bahrain to clamp down on opponents.”

Tiny but strategic Bahrain, which is home to the US Navy’s Fifth Fleet, has been rocked by unrest since a 2011 Shiite-led uprising demanding a constitutional monarchy and more representative government.

At least 89 people have been killed in clashes with security forces since 2011, while hundreds have been arrested and put on trial, rights groups say.