Rights groups have condemned the recent arrests by Saudi authorities of dozens of prominent religious figures, intellectuals and activists this week as "a coordinated crackdown on dissent".

The arrests were made in advance 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.

On Sunday, online activists said up to 20 influential Saudi religious scholars had been arrested, including some of the kingdom's most influential preachers.

Two days later, there were reports of more detentions of preachers and scholars.

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Human rights NGO Amnesty International on Friday voiced concern over the arrests.

"In recent years, we cannot recall a week in which so many prominent Saudi Arabian figures have been targeted in such a short space of time," Amnesty's Samah Hadid said.

The organisation said the rights situation in the Gulf state had "deteriorated markedly" since Prince Mohammed bin Salman took over as crown prince and heir to the throne on June 21.

US-based group Human Rights Watch (HRW) also suggested the arrests could be connected to the prince's efforts to consolidate power.

"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, HRW's Middle East director.

Whitson added: "Outlandish sentences against peaceful activists and dissidents demonstrate Saudi Arabia's complete intolerance toward citizens who speak out for human rights and reform."

Activists this week circulated on social media lists of people detained, including prominent Islamic preachers Salman al-Awdah and Awad al-Qarni, as well as some people with no clear links to Islamist activity or obvious history of opposition.

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

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

The detentions follow widespread speculation, denied by officials, that King Salman bin Abdulaziz Al Saud intends to abdicate to his son, Crown Prince Mohammed, who dominates economic, diplomatic and domestic policy.

The Saudi authorities have not commented on the latest arrests of activists.

But at the start of the week, the attorney general warned that any attack on "national unity" or the "image of the state" amounted to a "terrorist crime".