The 11 women on trial had campaigned for the right to drive and an end to the kingdom’s male guardianship system.
Their case has intensified Western criticism of Saudi Arabia’s rights record, already in the spotlight after last year’s murder of journalist Jamal Khashoggi by Saudi agents.
The U.S. nationals are journalist Salah al-Haidar, whose mother Aziza al-Yousef is among those on trial, and Bader al-Ibrahim, a doctor and author of a book about Shi’ite Muslim politics, the associate and London-based Saudi rights group ALQST said.
Those newly detained are not frontline activists but have expressed support online of women’s rights and other reforms in the conservative kingdom.
They were picked up on Thursday, according to ALQST and the associate, who was speaking on condition of anonymity.
Several other people close to the women have also been placed on travel ban since February, they added.
The Saudi government communications office and the U.S. Embassy in Riyadh did not immediately respond to requests for comment.