The rights group has been informed that on 12 May, armed security agents conducted a raid on the home of Abdulrahman al-Jabri, an engineering professor at King Saud University, detaining him without explanation and without informing any of his relatives.

The campaign to force al-Jabri back to the country is likely linked to the crackdown on Mohammed bin Nayef and Ahmed bin Abdulaziz al-Saud, a brother of King Salman, who are allegedly accused of plotting a coup against the crown prince.

However HRW says it is probable that the royals have been detained as punishment for complaining privately about Mohammed bin Salman.

In a bizarre incident earlier this month, the Saudi General Directorate of Prisons posted a tweet denying reports that bin Nayef had died, saying he had been hospitalised after suffering a heart attack.

However the tweet was swiftly deleted and the government issued a statement saying the Twitter account had posted "incorrect information" after being hacked.

Arbitrary arrests of fellow royals and critics has become a pattern Mohammed bin Salman's rule, despite his pledges to liberalise the kingdom through his flagship Vision 2030 programme of reforms.

Since deposing bin Nayef in 2017, Mohammed bin Salman has centralised power to an unprecedented degree, imprisoning swathes of critics and executing hundreds of opponents.

"Saudi Arabia’s recent justice reforms have not curbed the authorities’ contempt for the rule of law, showing the country needs a full overhaul of the justice and security sectors," Page said.

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