Amnesty International has accused Saudi Arabia of conducting a campaign of repression against protesters and reformists since the Arab Spring erupted, in a newly published report.
"The last nine months has seen a new wave of repression in Saudi Arabia as authorities have cracked down on protesters and reformists on security grounds," the rights watchdog said in a statement issued late Wednesday.
Philip Luther, Amnesty's director for the Middle East and North Africa, said peaceful protesters had been targeted in a bid to "stamp out the kinds of call for reform that have echoed across the region."
"While the arguments used to justify this wide-ranging crackdown may be different, the abusive practices being employed by the Saudi Arabian government are worryingly similar to those which they have long used against people accused of terrorist offences," he said.
Saudi Arabia has been spared much of the unrest that has swept the Arab world this year and toppled autocratic leaders in three countries -- Tunisia, Egypt and Libya.
And Amnesty accused the authorities in the conservative Sunni kingdom of detaining "thousands of people, many of them without charge or trial, on terrorism-related grounds."
"Torture and other ill-treatment in detention remains rife," said the London-based rights group.
In April, a judicial source said, 5,080 "terrorist" suspects either faced trial or had already been tried before a special Saudi security court which has come in for criticism from lawyers.
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Saudi Arabia witnessed a wave of deadly Al-Qaeda attacks between 2003 and 2006, prompting authorities to launch a security crackdown on the local branch of the jihadist network.
Amnesty also accused the Gulf state of having "carried out a crackdown that included the arrest of hundreds of mostly Shiite Muslims in the restive Eastern Province."
Shiites in the oil-rich region have rallied since March in support of their fellow believers in Bahrain, where democracy protests were crushed in March with backing by troops from Saudi Arabia and other Gulf states.
Last month, four Shiites were shot dead during clashes between protesters and security forces in the same region. The interior ministry said two policemen were wounded.
Amnesty said 300 people who took part in the protests were detained.
"Most have been released, often after pledging not to protest again," said the watchdog, adding that "many face travel bans."
"Elsewhere in the country, protests have been stifled by warnings by the Interior Ministry that the authorities would 'take all necessary measures' against those who tried to 'disrupt order'."
Amnesty described as "grossly unfair" the trial of 16 men including nine prominent reformists who were sentenced to jail for up to 30 years after being found guilty on November 22 of charges including attempting to seize power.
The rights group alleged Saudi authorities had drafted a secret law that would allow them to "prosecute peaceful dissent as a terrorist crime and permit extended detention without charge or trial."