More than 100 Saudi clerics have signed a petition calling for fair hearings for prisoners held on security grounds in the conservative kingdom, which has arrested thousands of people in a campaign against Islamist militants.
The petition, prompted by the detention earlier this month of 11 women who staged a protest to demand the release of jailed relatives, also called on the authorities to treat women prisoners properly.
Rights groups say thousands have been detained in the name of security in Saudi Arabia, many of them imprisoned without a fair hearing or held for long periods without trial. They say some were detained merely for demanding political change.
The authorities deny holding political prisoners and say all those detained for reasons of security are suspected Islamist militants. They said over 5,000 people were detained last year in a crackdown on the militants and most had already been tried.
Conservative Sunni Muslim clerics hold powerful positions in Saudi Arabia, the birthplace of Islam. However, some have also opposed the ruling family on issues ranging from social reform to the campaign against Islamist radicals.
The 100 clerics who signed the petition are from Qassim, one of the most conservative parts of Saudi Arabia and the heartland of its austere Wahhabi school of Sunni Islam.
Activists familiar with the petition said those who signed it were from a variety of ideological backgrounds, suggesting they may include both Islamists and comparative liberals.
"The issue of detainees has become the community's issue," the petition read. "The releases occurring are less than the (number) expected, which has resulted in growing frustration among the people."
"This has become evident through the protests and sit-ins that are increasing in number and widening in scope and intensifying in tone... It would be wise to resolve this issue quickly," it added.
The protest in which the 11 women were detained on January 5 is the latest in a string of small-scale demonstrations and sit-ins outside government offices in Qassim and the capital Riyadh over the past 18 months.
In September the then interior minister Prince Ahmed said no further protests about detainees would be tolerated.
All protests in Saudi Arabia, the world's top oil exporter, are illegal. The government says it does not mistreat prisoners.
The petition said Islam forbids the mistreatment of women. The detention of women is particularly sensitive in more conservative parts of Saudi Arabia, such as Qassim.
The crackdown against Islamist militants came in response to a series of attacks by al Qaeda on government and Western targets from 2003 to 2005. The militants were crushed inside the kingdom but some fled to Yemen where they set up a new wing of al Qaeda that swore to bring down the Saudi ruling family.
(Additional reporting by Angus McDowall; Editing by Tom Pfeiffer)