The protests, which took place Friday, were triggered by the arrest of a total of eight activists and preachers during the week ahead of parliamentary elections in the island kingdom.

"They set tires, garbage skips, empty water tanks and private property on fire, in addition to hurling firebombs on roads," Bahrain's Gulf Daily News quoted an unidentified security officer as saying.

The newspaper said protesters damaged an electricity substation, causing power outages for several hours.

Bahrain has a sizable Shiite population that complains of discrimination in jobs and services. The government denies the accusation.

Diplomats say the arrests appeared to be an effort to push the opposition to temper protests ahead of parliamentary elections due Oct. 23.

Bahrain has the only elected Parliament in the Gulf besides Kuwait, even though its powers are limited as bills need to be approved by an upper house whose members are appointed by the king.