Rothna Begum, a women's rights researcher for New York-based Human Rights Watch, dismissed Monday's event as a publicity stunt intended to deflect criticism.

"Now we have videos of traffic police handing over these driver's licences to divert the world's attention from the fact that the women who were actually behind championing the cause ... are not only in prison but have been charged and potentially face very, very long sentences," she said.

At least 17 activists were arrested on suspicion of trying to undermine the kingdom's security and stability, a case that local rights activists said has primarily targeted individuals who advocated for women's rights.

They include women who were arrested before for driving in Saudi Arabia in defiance of the ban and also lobbied for the lifting of restrictions requiring women to obtain the permission of a male guardian before marrying, travelling abroad or getting released from prison.

Eight were temporarily released, pending the completion of a procedural review, the Saudi Public Prosecutor's Office said in a statement on Sunday. Nine others - four women and five men - remain in custody and face possible trial.

The detainees were said to have admitted to serious charges, including communicating and cooperating with individuals and organisations "hostile to the kingdom," recruiting "persons in a sensitive government entity to obtain confidential information and official documents to harm the higher interests of the kingdom" and providing financial and moral support to "hostile elements abroad".

Activists convicted on similar charges are currently serving between eight and 10 years in prison, Begum said.

Saudi prosecutors did not publicly identify the suspects who remain in custody. But Amnesty International and Human Rights Watch said they include three women who are among the most prominent proponents for allowing everyone to drive: Loujain al-Hathloul, Aziza al-Yousef, and Eman al-Nafjan.

State-backed media accused the detainees of betraying their country and acting as "agents of embassies." One pro-government Twitter account posted images of some of them with the word "traitor" written in red across their faces.

Activists said their treatment shows that for all the social and economic reforms, there is still no tolerance for dissent in Saudi Arabia.

"This is a kingdom that bans protests, that bans independent human rights organisations and trade unions," Begum said. "This has not changed under Mohammed bin Salman. If anything, since his ascent to power, the situation has become more repressive for human rights defenders."

Even some staunch supporters of the crown prince suggest that the government may have erred in arresting the women.

"My understanding is that they broke the law technically in something they did, which was not really directly related to their activism," said Ali Shihabi, founder of the Washington-based Arabia Foundation. "But I still think that this was maybe an overreaction."

He said the 32-year-old prince has done more than any king in the last 50 years to advance women's rights in Saudi Arabia - an effort that has required him to push back against a "very strong, conservative, reactionary part of society that has been resisting these changes for decades."

Shihabi said officials may have wanted to show that they aren't only cracking down on conservative clerics and their supporters, who have also faced arrest in recent years.

"The government is very nervous (about) balancing different elements of society as it's pushing for disruptive change," he said.

At the same time, he added, the government does not want to be seen as implementing a "Western agenda".

"Because these women are so Western and liberal, and they are being feted in the West ... they help give meat to that narrative with Saudi conservative public opinion," Shihabi said. "In the view of the crown prince, this is in the interests of Saudi Arabia. It's not because Uncle Sam has asked him to do this."