Saudi Arabia's public prosecutor is seeking the death penalty against five human rights activists, including, for the first time a woman, campaigners say.
The five stand accused of inciting mass protests in mainly Shiite areas of the Sunni-ruled kingdom's oil-rich Eastern Province and human rights groups charged that the execution threat was a calculated bid to stifle dissent.
It comes as Saudi Arabia takes an increasingly combative approach to international criticism of its human rights record, imposing a raft of sanctions against Canada after it spoke out earlier this month.
Female activist, Israa al-Ghomgham, who has documented the protests in Eastern Province since they began in 2011, would be the first woman activist to face the death sentence for rights-related work.
She was arrested at her home along with her husband in December 2015, Amnesty International and Human Rights Watch said in separate statements this week.
"Israa al-Ghomgham and four other individuals are now facing the most appalling possible punishment simply for their involvement in anti-government protests," said Samah Hadid, Amnesty International's Middle East director of campaigns.
"We are urging the Saudi Arabian authorities to drop these plans immediately."
Saudi officials did not immediately respond to a request for comment.
HRW said Ghomgham, her husband and the three other defendants face charges that "do not resemble recognisable crimes".
"Any execution is appalling, but seeking the death penalty for activists like Israa al-Ghomgham, who are not even accused of violent behaviour, is monstrous," its Middle East director Sarah Leah Whitson said.
- 'Horrifying message' -
Amnesty said the unprecedented call for a death sentence against Ghomgham was a clear attempt to scare other dissidents into silence.
"Sentencing Israa al-Ghomgham to death would send a horrifying message that other activists could be targeted in the same way for their peaceful protest and human rights activism," Hadid said.
Amnesty says at least 12 other leading activists, including eight women, have been arrested in the kingdom since May -- just before the authorities ended their decades-long ban on women driving.
Many of them had opposed both the driving ban and the wider system of statutory male "guardians" for women -- fathers, husbands or other relatives, whose permission is required to travel or get married.
Earlier this month, Canada sparked fury in Riyadh by calling for the "immediate release" of the detained activists, including award-winning women's rights campaigner Samar Badawi.
Saudi Arabia froze all new trade and investments, moved to pull out thousands of Saudi students from Canadian universities and pledged to stop all medical treatment programmes in Canada. State airline Saudia also suspended flights to Toronto.
The ultra-conservative kingdom has one of the world's highest rates of execution, with suspects convicted of terrorism, homicide, rape, armed robbery and drug trafficking facing the death penalty.
Human rights groups have repeatedly raised concerns about the fairness of trials in the kingdom, an absolute monarchy governed under a strict form of Islamic law. The government says the death penalty is an effective deterrent against serious crime.