RIYADH (AFP) - Saudi Arabia's interior ministry said on Saturday that protests were illegal, amid various calls for demonstrations demanding change in the ultra-conservative kingdom, state media said.
"Regulations in the kingdom forbid categorically all sorts of demonstrations, marches and sit-ins ... as they contradict Islamic sharia law and the values and traditions of Saudi society," said a statement carried by SPA state news agency.
Police are "authorised by law to take all measures needed against those who try to break the law," the statement added.
On Friday, several hundred Shiites protested in Eastern Province, calling for the release of an arrested Shiite cleric, Sheikh Tawfiq al-Aamer, and other detainees, witnesses said.
The demonstration was staged after an appeal made on Facebook for a "Day of Rage" in the kingdom's east to demand the release of Aamer, who was arrested on Sunday.
Hundreds of people demanded the detainees' release after Friday prayers in the town of Al-Hufuf, witnesses said.
A similar protest was held in Al-Qatif, also in Eastern Province, but was dispersed by police, witnesses said.
On Thursday night, 22 people were arrested as police dispersed a rally in Al-Qatif in which protesters demanded the release of prisoners, said Ibrahim al-Mugaiteeb, the head of Human Rights First in Saudi Arabia.
"The protesters demanded the liberation of nine 'forgotten' prisoners in Al-Qatif, and also of Sheikh al-Aamer, whose picture they carried, and called for national unity between Sunnis and Shiites," Mugaiteeb told AFP by telephone.
Aamer was arrested "after calling for the establishment of a constitutional monarchy" in the kingdom, which is currently ruled by an absolute monarch, according to the website www.rasid.com, which specialises in information on Saudi Shiites.
On Friday, a dozen men gathered at the exit of Riyadh's Al-Rajhi mosque, one of the capital's most important, repeating slogans denouncing "oppression" and the monarchy, according to witnesses.
Three men were arrested, witnesses said.
Activists have called on Facebook for a "Day of Rage" on March 11 and for a "Saudi revolution" on March 20.
The calls came after several petitions from intellectuals and activists were addressed to King Abdullah urging him to introduce major reforms, including establishing a constitutional monarchy, allowing elections and improving women's rights.
On the Saudi stock market -- the Arab world's largest -- the Tadawul All-Share Index (TASI) closed 7.26 percent higher on Saturday after shedding 15 percent last week as fears of uprisings spreading through the region shook Arab financial markets.
The tide of demonstrations in several Arab countries gained momentum after the ouster of Tunisian president Zine El Abidine Ben Ali in January and Egypt's president Hosni Mubarak last month.