(Reuters) - The campaign group Human Rights Watch on Friday condemned the arrest by Saudi authorities of some 30 clerics, intellectuals and activists this week as a “coordinated crackdown on dissent”, and Amnesty International echoed the sentiment.

The arrests were made after exiled opposition figures called for demonstrations following Friday’s 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. They included prominent Islamist preacher Salman al-Awdah, as well as some people with no clear links to Islamist activity or obvious history of opposition.

The detentions come amid widespread speculation, denied by officials, that King Salman, 81, intends to abdicate in favor of his son, Crown Prince Mohammed, who dominates economic, foreign and domestic policy.

There are also growing tensions with Qatar over its alleged support of Islamists, including the Muslim Brotherhood, which is listed by Riyadh as a terrorist organization.

“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 group said the arrests fitted a pattern of human rights violations against peaceful activists 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 aimed at weaning the country off oil and introducing social reforms. Critics say he is not doing enough to liberalize politics in a country where the king enjoys absolute authority.

Amnesty International also denounced the crackdown, urging the authorities to reveal the whereabouts of the detainees and give them access to families and lawyers.

“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,” said Samah Hadid, the group’s director of campaigns in the Middle East.

“It is clear that the new leadership under Crown Prince Mohammed Bin Salman is sending a chilling message: freedom of expression will not be tolerated, we are coming after you.”

A government spokesman did not immediately respond to a request for comment.

CALL FOR PROTESTS

All public protests are banned in Saudi Arabia, as are political parties. Labor unions are illegal, the media are controlled and criticism of the royal family can lead to prison.

Riyadh says it does not have political prisoners, but senior officials have said monitoring of activists is needed to maintain social stability.

The al-Saud family has always regarded Islamist groups as the biggest internal threat to its rule over a country in which appeals to religious sentiment cannot be lightly dismissed and an al Qaeda campaign a decade ago killed hundreds.

Islamist movements such as the Muslim Brotherhood, which originated in Egypt and briefly held power there after the 2011 Arab Spring, represent an ideological threat to Saudi Arabia’s dynastic system of rule.

The Brotherhood-inspired Sahwa movement agitated in the 1990s to bring democracy to Saudi Arabia and criticized the ruling family for corruption, social liberalization and working with the West, including allowing U.S. troops into the kingdom during the 1991 Iraq war.

The Sahwa were weakened by a mixture of repression and co-optation, but remain active.

Saudi Arabia, the United Arab Emirates, Bahrain and Egypt cut diplomatic and transport links with Qatar in June over its alleged support for Islamists including the Brotherhood -- a charge Doha denies.

At a mosque in central Riyadh that protest organizers had identified as one of several potential gathering spots, the imam warned worshippers against demonstrating.

“All the groups that exist today and call for political action or aspire to rule -- they are all misguided, deviant groups headed by the Muslim Brotherhood,” he said.

Most people seemed to heed that message, with no demonstrations reported across the kingdom.