Hatoon Ajwad al-Fassi, a prominent women's rights advocate and a writer at the Riyadh paper was arrested on Wednesday according to reports circulated on social media.
Under the hashtag "embassy agents" Saudi social media users praised on Twitter the arrest of Fassi.
Saudi Arabia is pursuing an "unrelenting crackdown on the women's rights movement", Human Rights Watch said following the arrest of two activists earlier this month.
Nouf Abdelaziz and Mayaa al-Zahrani were arrested following the detention of at least 14 other women's rights campaigners and supporters.
The kingdom has led a vicious media campaign against those arrested. Saudi Arabia has described the activists as "traitors" in commentary condemned by Amnesty International as a "chilling smear campaign" and an "extremely worrying development for women human rights defenders" in the country.
Referring to the detainees as "agents of the [enemy] embassies", political analyst Naif al-Asaker tweeted that anyone who did not support their arrest was either a "covert partner" or simply "ignorant".
"Social media led a coordinated and vicious campaign branding them as traitors, as collaborators," said Zayadin, a researcher at HRW.
"On the front pages of news outlets, accused of suspicious contact with hostile elements. We've seen these types of accusations before, a vague catch all used to suppress all dissent."
Nine suspects - including four women - remain in custody after they "confessed" to a slew of charges such as suspicious contact with "hostile" organisations and recruiting people in sensitive government positions, according to the official Saudi Press Agency.
The arrests come along a much anticipated lift of the driving ban on women.
Crown Prince Mohammed bin Salman's announcement last year that women would be allowed to drive from 24 June was hailed from some sections of international media.
Analysts have warned that the reforms are merely cosmetic changes, allowing the kingdom to attract positive international publicity, while it continues its crackdown on activists.
This article has been adapted from its original source.
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