Joe Stork, the New York-based rights NGO’s deputy Middle East director, lashed out at the Arab sheikdom in a statement on Thursday for its treatment of Sheikh Ali Salman, the secretary general of Bahrain's main opposition bloc al-Wefaq National Islamic Society, and Ibrahim Sharif, the secretary general of the National Democratic Action Society (Wa'ad), the country’s largest leftist political party.

"Salman and Sharif have consistently supported peaceful political reform and should be at a negotiating table with Bahrain's government, not languishing behind bars," said Stork, who called them “unjustly imprisoned” figures.

Shia cleric Salman was arrested on December 28, 2014 after Manama accused him of seeking regime change and collaborating with foreign powers. 

Sharif was released from prison on June 19 after spending four years in jail over his involvement in the popular uprising, which began in the country in 2011. Opposition sources said Sharif was rearrested after he criticized the Bahraini regime during a memorial ceremony for a victim of the unrest in the kingdom. He is accused of “promoting political change through forceful means and threats and inciting hatred against the political regime.”

Both regime opponents will face new hearings in their trials next week.

Bahrain, a close ally of the United States in the Persian Gulf region, has been witnessing almost daily protests against the ruling Al Khalifa dynasty since mid-February 2011.

Bahrain's ongoing heavy-handed crackdown on peaceful demonstrations has left scores of people dead and hundreds injured.

Stork, meanwhile, called on the regime’s allies, Washington and London, to intervene in the case.

The United States and Britain "are fully aware of the gross unfairness of Salman's trial and the content of Sharif's peaceful speeches, and this should give them good reason to call publicly for an end to their prosecutions and their immediate release”; Press TV reported.