Human Rights Watch condemned a “coordinated crackdown on dissent” by Saudi authorities who have arrested dozens of people including prominent clerics in the ultra-conservative kingdom.

The New York-based watchdog described the detentions as politically motivated, noting that since 2014 Saudi Arabia has tried nearly all peaceful dissidents in its terrorism tribunal, the Specialised Criminal Court.

“Outlandish sentences against peaceful activists and dissidents demonstrate Saudi Arabia’s complete intolerance toward citizens who speak out for human rights and reform,” said HRW’s Middle East director Sarah Leah Whitson.

According to activists, at least 20 people including prominent clerics Salman al-Awdah and Awad al-Qarni have been arrested by the Saudi authorities since September 9.

HRW has said that the arrests could be connected to efforts by Saudi crown prince Mohammed bin Salman to consolidate power.

Awdah and Qarni, who have millions of followers on social media, were among Saudi clerics who opposed the presence of US troops in the kingdom during the 1991 Gulf war.

They have both been accused of links to the Muslim Brotherhood, which Saudi Arabia has blacklisted as a “terror group”.

Before his arrest, Awdah had welcomed the first contact between Prince Mohammed and Qatar’s emir Sheikh Tameem bin Hamad Al-Thani after a three-month boycott.

Saudi Arabia, the United Arab Emirates, Bahrain and Egypt severed all ties on June 5 and imposed economic sanctions on Qatar, accusing it of links to extremist groups and the Muslim Brotherhood.

The Saudi authorities have not commented on the campaign of arrests.

But at the start of the week the attorney general warned that any attack on “national unity” or the “image of the state” was a “terrorist crime”.