Saudi Arabia warned potential protesters on Saturday that a ban on marches would be enforced, signaling the small protests by the Shi'ite minority in the oil-producing east would no longer be tolerated.
"The kingdom's regulations totally ban all sorts of demonstrations, marches, sit-ins," the interior ministry said in a statement, adding security forces would stop all attempts to disrupt public order.
Inspired by protests in other Arab countries there have been Shi'ite marches in the past few days in the east and unconfirmed activist reports of a small protest at a mosque in the Saudi capital Riyadh on Friday.
More than 17,000 have backed a call on Facebook to hold two demonstrations this month, the first one on Friday.
A loose alliance of liberals, moderate Islamists and Shi'ites have petitioned King Abdullah to allow elections in the kingdom which has no elected parliament, although even activists say they don't know how many of the almost 19 million Saudis back them.
Last month, Abdullah returned to Riyadh after a three-month medical absence and unveiled $37 billion in benefits for citizens in an apparent bid to curb dissent.
For about two weeks, Saudi Shi'ites have staged small protests in the kingdom's east, which holds much of the oil wealth of the world's top crude exporter and is near Bahrain, scene of protests by majority Shi'ites against their Sunni rulers.
Shi'ite protests in Saudi Arabia started in the area of the main city Qatif and its neighbor Awwamiya and spread to the town of Hofuf on Friday. The demands were mainly for the release of prisoners they say are held without trial.
Saudi Shi'ites often complain they struggle to get senior government jobs and other benefits like other citizens.
The government of Saudi Arabia, an absolute monarchy without an elected parliament that usually does not tolerate public dissent, denies these charges.
The interior ministry said demonstrations violated Islamic law and the kingdom's traditions, according to a statement carried by state news agency SPA.