Hundreds of Saudi Shi'ites staged a protest in the kingdom's oil-producing Eastern Province on Friday calling for prisoner releases and a withdrawal of Saudi forces from Bahrain, activists said.

The world's No. 1 oil producer and a U.S. ally, Saudi Arabia has not seen the kind of mass uprisings that have rocked the Arab world this year. But dissent is simmering in the kingdom as unrest takes root in neighbouring Yemen, Bahrain and Oman.

There were rallies in two villages close to the main Shi'ite centre of Qatif shortly after midday and afternoon prayers.

"There are around 400 protesters here at the moment and some are waving Bahraini flags," said one protester who declined to be named. "The protests are peaceful and the riot police are well away from the demonstrators."

Demonstrators called for political freedoms and an end to what they call sectarian discrimination against Saudi Arabia's Shi'ite Muslim majority by the absolute Sunni monarchy.

Saudi Shi'ites have held a number of protests in Eastern Province, where most of the country's oil fields are.

A Saudi human rights group said on Wednesday authorities arrested 100 protesters last week in the Shi'ite populated areas of Safwa, Qatif and its villages and Hasa.

Saudi Shi'ites complain of discrimination, saying they often struggle to get senior government jobs and benefits available to other citizens. The government of Saudi Arabia, a monarchy that usually does not tolerate public dissent, denies such charges.

Almost no Saudis in major cities answered a Facebook call for protests on March 11, in the face of a massive security presence around the country.

Dozens of Saudi men gathered outside the Interior Ministry in the capital Riyadh on Sunday to demand the release of jailed relatives.

King Abdullah last week offered $93 billion in handouts and boosted his security and religious police forces but did not make concessions on political rights.

Saudi Arabia has sent 1,000 troops to Bahrain, also a Sunni monarchy, to help contain pro-democracy protests led by that Gulf Arab country's Shi'ite majority.