Arrested Munir al Jassas, Muhammad al Lebbad and Ramzi Jamal
* Saudi Shi'ites hold small protest, Shi'ites sources say
* Saudi Arabia is worried Bahrain protest could spread
Saudi Shi'ites have held a small protest in the kingdom's oil-producing eastern province, close to Gulf Arab neighbour Bahrain where unrest has cost six lives, local Shi'ite sources said on Saturday.
They said a group of Shi'ites staged a protest on Thursday in the town of Awwamiya, near the Saudi Shi'ite centre of Qatif on the Gulf coast, to demand the release of fellow Shi'ites held in prison without trial.
Top OPEC exporter Saudi Arabia fears that unrest in Bahrain, where majority Shi'ites are protesting against the Sunni government, might spread to its Shi'ite minority who mostly live in the eastern province, the source of Saudi oil wealth.
Shi'ite website Rasid.com said protesters gathered in the centre of the small town but stayed silent and did not hold up any posters to avoid provoking the authorities.
Saudi Arabia applies an austere Wahhabi version of Sunni Islam and minority Shi'ites say that, while their situation has improved under reforms launched by King Abdullah, they still face restrictions in landing senior government jobs.
Awwamiya, a town visibly less affluent than the rest of the country, was the scene of protests for weeks in 2009 after police launched a search for firebrand Shi'ite preacher Nimr al-Nimr, who breached a taboo to suggest in a sermon that Shi'ites could one day seek their own separate state.
The threat, which analysts say was unprecedented since the 1979 Iranian revolution provoked anti-Saudi protests, followed clashes between the Sunni religious police and Shi'ite pilgrims near the tomb of Prophet Mohammad in the holy city of Medina.
Since then Saudi Shi'ites say the situation has calmed down but they are still waiting for many reform promises to be carried out.
Officials say Shi'ites make up 10 percent of the Saudi population, though diplomats put it closer to 15 percent. (Reporting by Ulf Laessing; editing by Tim Pearce)