CAIRO -- Saudi police opened fire Thursday to disperse a protest in the section where minority Shiites live, leaving at least one man injured, as the government toughened its efforts to prevent a wave of unrest sweeping the Arab world from reaching the kingdom.

The rare violence raised concern about a crackdown ahead of planned protests after Friday prayers in different cities throughout the oil-rich kingdom. Violence there could reverberate through the world's markets because of the importance of Saudi oil exports.

Discord is common between authorities and the country's Shiites, who make up 10 percent of the kingdom's 23 million citizens. They have long complained of discrimination, saying they are barred from key positions in the military and government and are not given an equal share of the country's wealth.

Eyeing rising discontent across the Middle East and North Africa, Saudi authorities are increasingly determined to prevent the unrest from spreading to other cities.

Saudi security forces have deployed around the capital of Riyadh on the eve of planned protests calling for democratic reforms.

Witnesses reported Thursday seeing riot police and special forces with batons and tear gas canisters, particularly around shopping malls and main roads.

The pro-Western monarchy is concerned protests could open footholds for Shiite powerhouse Iran and has accused foreigners of stoking the protests, which are officially forbidden.

Despite the ban and a warning that security forces will act against them, protesters demanding the release of political prisoners took to the streets for a second day in the eastern city of Qatif.

Several hundred protesters, some wearing masks to avoid being identified, marched after dark asking for "Freedom for prisoners."

Police, who were lined up opposite the protesters, fired percussion bombs followed by gunfire, causing the crowd to scatter, a witness said, speaking on condition of anonymity for fear of government retaliation.

The witness said at least one protester was injured and lifted by others to a car for treatment. It was not clear how the protester was hurt.

A resident, contacting The Associated Press by e-mail, said the Saudi authorities also beat some protesters with clubs. The resident said up to 12 protesters were injured, and some were arrested at the local hospital.