Protest rallies rage on in�Saudi Arabia's Eastern Province, raising the specter of wider unrest in�the important oil-rich region.�

Since Saturday's execution of prominent cleric�Sheikh Nimr and three other Shia�Muslims, hundreds or thousands of people�have marched nightly in protest.

"People are angry. And they are surprised, because there were positive signals in the past months that the executions would not take place. People listen to his speeches and there's no direct proof he was being violent," a Qatif community leader told Reuters.

Qatif�in the oil-rich�province is enormously tense,�where people see the executions as unjustified. Shouting "down with the Al Saud,"�the marchers continue to�denounce the�execution.

Hundreds of anti-riot personnel carriers set off for Qatif on Saturday to quell any potential unrest.�Security forces have also been alerted in other Shia-populated cities across Saudi Arabia.

The protests in the city of�about one million people�have been mostly peaceful.�However, a fatal shooting and gun attacks on armored security vehicles have also taken place so far.

The Shia-dominated�Eastern Province has been the scene of peaceful demonstrations since February 2011.

Protesters have been demanding reforms, freedom of expression and the release of political prisoners. They want an end to economic and religious discrimination against the region.

Many of the residents of Qatif, located near major oil facilities, work for the state energy company, Saudi Aramco.

Past protests have not led to attacks on the oil industry, but a bus used by Aramco to transport employees was set ablaze during a Tuesday night rally.

Reports on protests in�Qatif are scant, as�Saudi authorities allow foreign�news media to visit the region if accompanied by government officials, claiming it is to ensure journalists' safety.

Locals, quoted by Reuters, said the protests may escalate depending on whether regime forces�allow�peaceful demonstrations to continue�or crack down with force.

Shia Muslims have long complained of�entrenched discrimination in a country where the semi-official Wahhabi school condones violence against them.

They face abuse from Wahhabi clerics, rarely get permits for places of worship and seldom get senior public sector jobs.

Those basic complaints have over the years been aggravated by what Qatif residents call a heavy security hand against their community

They accuse�the authorities of unfair detentions and punishments, shooting unarmed protesters and torturing suspects.

Reuters said it has met several Saudi Shias detained after the 2011 protests who said they were repeatedly beaten and deprived of sleep to extract confessions of rioting.

By Press TV