(CNN) -- Amnesty International is urging Saudi Arabia to stop the "outrageous restriction" of peaceful protests, a call that comes after a crackdown last week on protesters in the country's Shiite region.
About 24 protesters were detained in the eastern city of Qatif last week as they denounced "the prolonged detention" of nine Shiite prisoners held without trial for more than 14 years, the human rights group said.
Police kicked and used batons to beat three protesters in what was an apparent peaceful demonstration, Amnesty said in a statement dated Monday.
"The Saudi Arabian authorities have a duty to ensure freedom of assembly and are obliged under international law to allow peaceful protests to take place," said Philip Luther, deputy director of the human rights group's Middle East and North Africa program.''
"They must act immediately to end this outrageous restriction on the right to legitimate protest."
There was no immediate reaction from the Saudi government to the Amnesty statement.
The protests in the majority Sunni kingdom occurred Thursday and Friday, and they've accompanied the calls across the Arab world for more freedom and democracy.
Rights activists have been urging the right to protest for months in the kingdom, which prohibits all kinds of public demonstrations, and they have been denied permission to assemble.
Lately, grass-roots ferment mirroring the unrest across the Middle East and North Africa has emerged, with a Facebook group calling for days of rage and Shiites taking to the streets. Activists have been calling for reform and the release of people jailed without charge or trial.
Saudi Arabia's Interior Ministry warned Saturday that its security forces will be "authorized to take all measures against anyone who tries to break the law and cause disorder," the ministry said, according to the country's state-run news agency.
Amnesty said the recent detentions came a week after a prominent Shiite cleric, Sheikh Tawfiq Jaber Ibrahim al-'Amr was arrested after a sermon calling for reforms in Saudi Arabia. He was released without charge Sunday.
Most of the protesters are believed to be held in a police station in Dhahran, an eastern city. Among them are activists who have protested arrests and discrimination against the minority Shiites.
"The Saudi authorities must investigate reports of beatings of protesters by security forces. They should also ensure that those detained are either charged with recognizable offences and tried fairly or released," Luther said.
"While in detention they must be protected from torture and other ill-treatment and given regular access to their family, lawyers and medical staff."
The Shiite activists in "prolonged detention" have been held in connection with the deadly 1996 bombing of a U.S. military complex in Khobar in which 20 people were killed and hundreds injured.
"According to reports, they were interrogated, tortured and denied access to lawyers together with the opportunity to challenge the legality of their detention," Amnesty said.