(Bloomberg) -- Saudi authorities have severed contact between some of the kingdom’s most prominent detainees and their families, escalating a crackdown on dissent that threatens to strain relations with Western allies.

Loujain Al-Hathloul, a women’s rights activist whose 2018 arrest made global headlines, hasn’t called her family since June 9, her sister said. Princess Basmah bint Saud — a royal family member imprisoned with her adult daughter — hasn’t contacted relatives since April, when her detention was made public on Twitter, according to people familiar with the matter. And Salman Al-Odah, a prominent religious cleric detained in 2017, made his last call on May 12, according to his son.

Most were previously allowed to make regular, even weekly, phone calls home. Now, they’ve fallen silent.

“I’m worried to the degree that I really am numb at this point,” said the cleric’s son, Abdullah Alaoudh, explaining that he’s heard from many others in the same situation. “They’re worried sick about their families, and whether there have been any coronavirus cases, and why the government is just keeping them in the dark.”

Meanwhile, Saudi officials are moving forward with another set of cases that have caused upset in the United States. A group of intellectuals and writers detained last year that includes two Saudi-American dual nationals — Salah Al-Haidar and Bader Al-Ibrahim — recently received their list of charges, according to three people familiar with the matter.

They’re expected to face trial in a court reserved for terrorism and other security-related cases, the people said.

The Saudi government’s Center for International Communication, which fields inquiries from foreign media, did not respond to requests for comment. Calls to the General Directorate of Prisons’ public relations department were not answered, while a request for comment sent to its official media email bounced back with an automated message that the inbox was full.

To their families, the detainees’ silence represents an unexpected escalation in Crown Prince Mohammed bin Salman’s crackdown on domestic critics. Dozens of princes, businessmen, clerics, academics and activists have been arrested in recent years, creating a climate of fear among some even as Prince Mohammed wins praise for opening up the kingdom economically, loosening social restrictions and granting women more rights.

The tightening noose is creating a new generation of Saudi dissidents and spurring increased advocacy abroad, causing potential embarrassment for the kingdom. Already, several Saudis in exile have hired American lobbyists or lawyers to push their cases into the spotlight in the period leading up to the U.S. election.

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Prince Mohammed has cultivated close ties with President Donald Trump and his son-in-law and senior adviser, Jared Kushner, getting a declaration of support even after U.S.-based Washington Post columnist Jamal Khashoggi was killed by Saudi agents at the kingdom’s consulate in Istanbul in 2018.

The 34-year-old prince’s unpredictable foreign policy and crackdown on critics have alienated other parts of the U.S. government, however, and drawn increasing condemnation from members of Congress.

Four United States senators on both sides of the aisle urged Trump in July to help secure the freedom of an exiled Saudi official’s children, calling it a “moral obligation” to stand by a man who aided American intelligence for years but whom Saudi authorities say is fleeing corruption charges.

A change in the White House could bring a change in approach toward Saudi Arabia’s domestic crackdown. Trump’s Democratic rival Joe Biden has called Saudi Arabia a “pariah” and threatened to stop the sales of American weapons to the kingdom and to hold it accountable for the killing of Khashoggi. Ties with Saudi officials were often cool under Trump’s predecessor Barack Obama, and Biden, who was vice president.

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In an interview with Bloomberg in 2018, Prince Mohammed said the cases of most detainees “have nothing to do with freedom of speech,” accusing them of links to foreign intelligence and extremism.

Since then, authorities have continued to detain Saudis across the political and religious spectrum, including a prominent economist and a Snapchat influencer.

Al-Hathloul, along with several other women’s rights activists, was put on trial on a slew of charges including campaigning for political change, insulting the kingdom’s reputation, and communicating with diplomats and foreign journalists, however her trial has been on hold for months. Saudi prosecutors are seeking the death penalty for Odah on a number of security-related charges, some related to comments he made online.

“I wouldn’t wish this even on my worst enemies,” said Areej Al Sadhan, whose family received a single call from her brother Abdulrahman since he was detained in March 2018. They believe his arrest was related to an anonymous Twitter account he operated, she said. The call, this February, lasted less than a minute — just long enough to let them know he was alive, she said.

The lack of contact is unusual in Saudi Arabia, where most detainees make semi-regular phone calls to their families, and are afforded occasional visits, once their initial interrogation period is complete. The website of the kingdom’s interior ministry describes a prisoner’s communication with family and friends as a key element in their rehabilitation.

At one point, authorities told families that there were “organizational issues” due to the coronavirus pandemic, according to Alia Al-Hathloul, Loujain’s sister. But nothing changed as the kingdom began to phase out its lockdown in May.

Her parents last saw Loujain in early March, before prison visits were halted due to the coronavirus, which has infected more than 300,000 people in Saudi Arabia. She used to make weekly calls.

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Many relatives are particularly concerned because two prominent detainees released this year died shortly after.

Abdullah Al-Hamid, an activist jailed under the late King Abdullah, had a stroke in April, and was transferred to a hospital where he died later that month, according to a June letter from several United Nations special rapporteurs to the government. The letter urged the government to respond to allegations that prison officials had delayed surgery recommended by doctors for Al-Hamid. Authorities have not commented.

Then came the late May release of Saleh Al-Shehi, a journalist detained in 2017 after a televised diatribe about alleged corruption in the royal court. By mid-June, he was in intensive care, relatives wrote on Twitter. He died July 20, after being infected with coronavirus, Saudi newspapers reported.

Al Sadhan said she’d tried every avenue to reach her brother.

“The silence is deafening,” she said. “All the doors are closed. We have no other option but to speak up.”

©2020 Bloomberg L.P.