The sister of jailed Saudi blogger Raif Badawi was arrested Tuesday by Saudi authorities, according to Amnesty International and Badawi's wife Ensaf Haidar.
Samar Badawi was accused of directing the Twitter account of her former husband, jailed rights activist Waleed Abu al-Khair, Haidar wrote on Twitter.
Raif Badawi was last month awarded the European Parliament's human rights prize for what Parliament President Martin Schultz described as his "defence of the right to think freely."
The 31-year-old man was arrested more than three years ago for criticizing the Saudi religious police and sentenced to 10 years in jail and 1,000 lashes for insulting Islam.
He received the first 50 lashes in January 2015. Subsequent lashes were suspended on health grounds, amid a global outcry at his punishment.
Abu al-Khair, who acted as Raif Badawi's defence lawyer and headed the Saudi Arabia Monitor of Human Rights, is currently serving a 15-year sentence on what Amnesty International described as "farcical" charges.
Amnesty said Tuesday's arrest of Samar Badawi in Jeddah was "further damning proof of the authorities’ intent to suppress all signs of peaceful dissent."
It comes 10 days after Saudi authorities executed dissident Shiite cleric Nimr al-Nimr, provoking a furious response from Shiite Muslims and an ongoing dispute with Shiite Iran, Riyadh's arch-rival for influence in the region.