Several women's rights activists arrested in Saudi Arabia have been brought to court on unknown charges after being detained in a crackdown last year.

Amnesty International says that those brought to court included Loujain al-Hathloul, who has said she was abused and threatened with death while in detention because of her activism.

The watchdog said others included Eman al-Nafjan and Aziza al-Yousef.

Saudi state media didn't immediately acknowledge the hearing on Wednesday.

Al-Hathloul's brother, Walid, as well as Amnesty, said their court appearance was moved to a criminal court from one specialized for terrorism cases.

Amnesty's Samah Hadid said it was "quite concerning that they are likely to be charged for simply defending women's rights."

The group has previously said several detainees have been beaten and tortured during interrogations.