Saudi Arabia accused of repression after Arab Spring
Amnesty International has accused Saudi Arabia of reacting to the Arab Spring by launching a wave of repression.
In a report, the human rights group said hundreds of people had been arrested, many of them without charge or trial.
Prominent reformists had been given long sentences following trials Amnesty called "grossly unfair".
So far unrest has largely been confined to the Shia minority in the east of the country.
The report comes a little more than a week after clashes in the eastern region of Qatif left four people dead - apparently the first deaths in this year's unrest.
Shia in the area have complained for years of economic discrimination and religious persecution, and were angered by the harsh suppression of Shia protesters in neighbouring Bahrain earlier this year. Saudi troops entered Bahrain to assist the authorities there.
'Blindfolded and handcuffed'
In its 73-page report published on Thursday, Amnesty accuses the Saudi authorities of arresting hundreds of people for demanding political and social reforms or for calling for the release of relatives detained without charge or trial.
The report says that since February, when sporadic demonstrations began - in defiance of a permanent national ban on protests - the Saudi government has carried out a crackdown that has included the arrest of mainly Shia Muslims in the restive Eastern Province.
Since March, more than 300 people who took part in peaceful protests in Qatif, Ahsa and Awwamiya in the east have been detained, Amnesty says. Most have been released, often after promising not to protest again. Many face travel bans.
Last week 16 men, including nine prominent reformists, were given sentences ranging from five to 30 years in prison. Amnesty said they were blindfolded and handcuffed during their trial, while their lawyer was not allowed to enter the court for the first three sessions.
"Peaceful protesters and supporters of political reform in the country have been targeted for arrest in an attempt to stamp out the kinds of call for reform that have echoed across the region," said Amnesty's Middle East and North Africa director, Philip Luther.
"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.
Amnesty says that the government continues to detain thousands of people on terrorism-related grounds. Torture and other ill-treatment in detention are widespread, it says - an allegation Saudi Arabia has always denied.
The BBC's Security correspondent Frank Gardner says Saudi Arabia has so far resisted the wave of change that has swept over much of the Arab world.
Our correspondent says the kingdom's ageing monarch, King Abdullah, has reacted by releasing billions of dollars into the security and religious establishments, two of the pillars that support his ruling Al-Saud family.
Amnesty says the government has drafted an anti-terror law that would effectively criminalise dissent as a "terrorist crime" and allow extended detention without charge or trial.
Questioning the integrity of the king would carry a minimum prison sentence of 10 years, according to Amnesty.
The four who died in Qatif last week were killed when security forces opened fire using live ammunition, an indication that tensions in the predominantly Shia Eastern Province continue to escalate.
The interior ministry said the four were "armed aggressors hiding among civilians." A ministry spokesman blamed "foreign parties" - usually code for Iran- for fomenting unrest.
But a Shia activist told the BBC that at least one of those killed was unarmed when he was shot dead at a checkpoint for failing to stop. The others died the following day as protests erupted at his funeral, he said.
"Rather than deal with legitimate demands, the government is taking the easy route and blaming everything on a conspiracy by the Iranians," said the activist, who asked not to be named for fear of repercussions.