DUBAI - Saudi authorities have arrested at least 20 people, including prominent clerics Salman al-Awdah and Awad al-Qarni, in an apparent crackdown on dissent, activists and family members have said.

The arrests started on September 9 and on Tuesday included six clerics and Awdah’s brother, Khaled, for apparently disclosing that his brother had been detained, activists said.

Khaled al-Awdah had confirmed on his Twitter account on Monday that his brother was in custody.

The leading cleric was arrested after he welcomed the first contact between Saudi crown prince Mohammed bin Salman 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.

They cited Doha’s longstanding support for the Muslim Brotherhood, blacklisted by the four Arab governments as a terrorist group, although not by Western governments or the United Nations.

Hopes raised by the contact of a thaw in the Gulf’s worst diplomatic crisis in decades were swiftly dashed as Saudi Arabia suspended any further dialogue.

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.

Qarni has been accused of links to the Muslim Brotherhood.

Prominent Saudi journalist and writer Jamal Khashoggi said that he was banned from writing in Saudi-owned newspaper Al-Hayat, apparently for defending the Brotherhood in tweets.

A Twitter account called Motakl (Detained) run by activists opposed to the Saudi government reported the names of at least 21 people who have been rounded up so far, most of them clerics.

The account cited unnamed sources as expecting the number of arrests to double in the coming days.

It launched a petition calling for the immediate release of the detainees.

Human Rights Watch said that it had no direct information on the arrests but that they could be connected to Mohammed bin Salman’s efforts to consolidate power.

“What I can say is that it is very reflective of Saudi Arabia’s approach to political or religious dissent,” HRW Middle East researcher Adam Coogle, told AFP. “Saudi Arabia has a horrendous record on freedom of expression and you can say things are getting worse,” he added.