As he languishes in a cell in Bulgaria, Saudi dissident Abd al-Rahman al-Khalidi dreads one thing more than any other: being flown back to his home country.

"In the event of deportation, I will be subjected to torture and long imprisonment, as I have worked with the opposition for years," Khalidi, a failed asylum-seeker, told AFP by phone from a detention centre in Sofia.

For Khalidi, 29, and other dissidents who fled after criticising the Saudi monarchy, such fears assumed new urgency following the extradition last month of their compatriot Hassan al-Rabie, who had sought temporary refuge in Morocco.

Rabie, who comes from a family of prominent dissidents and stands accused of crimes including "collaboration with terrorists", has not been heard from since. Human rights groups warn he faces "serious rights abuses" on Saudi soil.

The case highlights the vulnerability of Saudi exiles amid a widening crackdown on dissent under Crown Prince Mohammed bin Salman, the oil-rich country's de facto ruler.

Critics accuse the 37-year-old of shrinking political space even as he pursues an ambitious reform agenda involving massive investments in sports and entertainment and the expansion of some rights for women.

People without political asylum or dual citizenship are "always at risk of deportation", said Taha al-Hajji, legal director of the European-Saudi Organisation for Human Rights.

- Nowhere to hide -

Khalidi's activism predates King Salman's ascent to the throne in 2015 and the appointment of Prince Mohammed as heir two years later.

In 2011, he was active during rare demonstrations in eastern Saudi Arabia, where the Shiite minority is concentrated, following the Middle East's Arab Spring uprisings.

He fled to Turkey in 2013 and watched as the long arm of the Saudi state tracked down more prominent activists who were also abroad.

That group includes Loujain al-Hathloul, a women's rights campaigner who was arrested in the United Arab Emirates in March 2018 and forced back to Saudi Arabia, where she spent more than two years behind bars.

In October 2018, Saudi agents killed and dismembered journalist and critic Jamal Khashoggi inside the kingdom's Istanbul consulate -- an operation US intelligence officials believe was "approved" by Prince Mohammed, despite Saudi denials.

Beyond these high-profile cases, notorious Saudi online surveillance operations -- which a US court found last year have included enlisting Saudi Twitter employees to unmask critics -- have also put exiles on edge.

So when Khalidi's passport expired in 2021, he sought protection in the European Union, fleeing on foot into Bulgaria.

His bid for asylum was unsuccessful, however, with authorities concluding in May that he had not adequately demonstrated he would face persecution back home, according to a Bulgarian lawyer who worked on the case and spoke on condition of anonymity.

A decision on Khalidi's possible extradition could come at any time.

Saudi authorities did not respond to questions from AFP about Khalidi's case and others like it.

- 'Never see the sun again' -

There are no comprehensive figures for Saudi dissidents living abroad, but activists and lawyers said popular destinations included the United States, Britain, Germany and Canada.

In the European Union, the number of Saudi asylum seekers has increased dramatically during King Salman's reign.

The bloc recorded 15 Saudi asylum seekers in 2013 and 40 in 2014, jumping to 130 in both 2017 and 2022, according to figures provided by the European Union Agency for Asylum.

Even those who obtain asylum say their fear never fully goes away.

Abdul Hakim al-Dakhil, a Saudi dissident who was arrested in 2010 after calling online for political reform, fled the kingdom in 2017, eventually ending up in France, where he was granted asylum in 2020.

"Before that, I was afraid that I would be deported, as I would be tried on fabricated charges, and I would never see the sun again," he told AFP.

He remains worried for his safety.

"I prefer being in public places, and I am still afraid to go to certain places on my own," Dakhil said.

Several Saudi dissidents and activists residing abroad told AFP they refuse to transit through Arab countries to avoid being extradited, as happened to Rabie.

"No one dares to pass" through the region, said Adel al-Saeed, vice-president of the European-Saudi Organisation for Human Rights.

Saudi activists consistently turn down invitations to human rights conferences in countries such as Lebanon and Tunisia for this reason, he added.

Lina al-Hathloul, Loujain's sister and head of monitoring for the London-based rights group ALQST, told AFP that asylum or dual nationality can offer a "layer of protection" for dissidents, but that there are limits.

"Taking into account the influence of Saudi Arabia on some countries," she said, "it is not a guaranteed protection".