Human Rights Watch today condemned the arrest by Saudi authorities of some 30 clerics, intellectuals and activists this week as "a coordinated crackdown on dissent".
The arrests were made ahead of a call by exiled opposition figures for demonstrations following Friday afternoon prayers, which did not appear to attract much support amid a heavy security deployment.
Activists this week circulated on social media lists of people detained, including prominent Islamist preacher Salman Al-Ouda, as well as some people with no clear links to Islamist activity or obvious history of opposition.
The detentions follow widespread speculation, denied by officials, that King Salman intends to abdicate to his son, Crown Prince Mohammed, who dominates economic, diplomatic and domestic policy.
There are also tensions with Qatar over its alleged support of Islamists, including the Muslim Brotherhood which is listed by Riyadh as a terrorist organisation because of the increase in its support base and threat to the monarchy's longevity.
"These apparently politically motivated arrests are another sign that Mohammed Bin Salman has no real interest in improving his country's record on free speech and the rule of law," said Sarah Leah Whitson, Middle East director at Human Rights Watch.
The New York-based watchdog said the arrests fit a pattern of human rights violations against peaceful advocates and dissidents, including harassment, intimidation, smear campaigns, travel bans, detention and prosecution.
Crown Prince Mohammed has rocketed to the pinnacle of power in the Kingdom, pushing a reform agenda called Vision 2030 which is aimed at weaning the country off oil and introducing social reforms. But critics say he is not doing enough to liberalise politics in a country where the King enjoys absolute authority.
"Saudis' alleged efforts to tackle extremism are all for show if all the government does is jail people for their political views," Whitson said.
A government spokesman did not immediately respond to a request for comment.