Saudi Arabiaâ€™s public prosecutor has reportedly sought the death penalty for five activists, including the female rights defender Israa al-Ghomgham.
Human Rights Watch said they recently went on trial at a terrorism tribunalÂ on charges including â€œparticipating in protestsâ€ in the restive Qatif region.
It has been the scene of demonstrations by the minority Shia Muslim community.
Ms Ghomgham is believed to be the first Saudi woman to possibly face the death penalty for rights-related work.
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HRW warned that it set â€œa dangerous precedent for other women activists currently behind barsâ€ in the Gulf kingdom.
At least 13 human rights defenders and womenâ€™s rights activists have been arrested since mid-May, accused of activities deemed a risk to national security. Some have been released, but others remain detained without charge.
HRW said Ms Ghomgham was an activist well known for participating in and documenting the mass protests that have taken place in Qatif since 2011.
Members of the Shia community have taken to the streets to complain about the discrimination they say they face
Ms Ghomgham and her husband were reportedly arrested in December 2015, and they have been held at Dammamâ€™s al-Mabahith prison ever since.
The public prosecutor accused Ms Ghomgham and the other four activists of charges including â€œparticipating in protests in the Qatif regionâ€, â€œincitement to protest,â€ â€œchanting slogans hostile to the regimeâ€, â€œattempting to inflame public opinionâ€, â€œfilming protests and publishing on social mediaâ€, and â€œproviding moral support to riotersâ€, according to HRW.
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â€œAny execution is appalling, but seeking the death penalty for activists like Israa al-Ghomgham, who are not even accused of violent behaviour, is monstrous,â€ Sarah Leah Whitson, HRWâ€™s Middle East director, said in a statement.
â€œEvery day, the Saudi monarchyâ€™s unrestrained despotism makes it harder for its public relations teams to spin the fairy tale of â€˜reformâ€™ to allies and international business.â€
The European Saudi Organisation for Human Rights and ALQST, a London-based Saudi human rights group, have called on the authorities to drop the charges against Ms Ghomgham.
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The Saudi government has so far not commented on Ms Ghomghamâ€™s trial.
However, courts have sentenced to death several Shia activists after convicting them of what human rights groups have called politically-motivated charges.
Officials have said those executed were guilty of terrorism-related offences, including taking up arms against the government and attacking security forces.