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Saudi Arabian authorities have arrested two high-profile women's rights activists, Human Rights Watch said Wednesday, amid what the organisation called an "unprecedented" crackdown on dissent.

Award-winning gender rights activist Samar Badawi was arrested along with fellow campaigner Nassima al-Sadah this week, "the latest victims of an unprecedented government crackdown on the women's rights movement," HRW said in a statement.

Their arrests "signal that the Saudi authorities see any peaceful dissent, whether past or present, as a threat to their autocratic rule," said Sarah Leah Whitson, Middle East director at Human Rights Watch.

Amal al-Harbi, the wife of jailed civic rights activist Fowzan al-Harbi, was also taken into custody this week, HRW said while adding that it was unclear why she was targeted.

Saudi authorities did not immediately respond to a request for comment.

The arrests come weeks after more than a dozen women's right campaigners were detained and accused of undermining national security and collaborating with enemies of the state. Some have since been released.

Samar Badawi is the recipient of the 2012 International Women of Courage Award, handed out by the US Secretary of State.

She is also a vocal campaigner for rights activist Raif Badawi, her brother and Saudi Arabia's top blogger, and Waleed Abu al-Khair, her former husband. Both men are serving lengthy jail terms for charges linked to their activism.

Like Badawi, Sadah is a longtime opponent of Saudi Arabia's guardianship system, under which women require male permission to study, marry or travel.

Saudi Arabia, a major US ally, has introduced a string of reforms over the past year aimed at improving the kingdom's image and oil-dependent economy.

Under the helm of Crown Prince Mohammed bin Salman, heir to the region's most powerful throne, Saudi Arabia in June ended a longstanding ban on women driving and launched a number of projects aimed at attracting tourists.