Saudi security forces opened fire on Shiite protesters in the tense Qatif district of Eastern Province on Friday, wounding several as hundreds marched to demand the release of detainees, witnesses said.
Live rounds fired by anti-riot police wounded a number of protesters who took to the streets in the early hours, the witnesses said, without specifying a figure.
The interior ministry said security forces dealt with "rioters who burned tyres" in parts of Qatif, arresting several people, including Mohammed al-Shakhuri, whose name figures on a list of 23 wanted people.
"There were no casualties," the ministry said in a statement carried by the official SPA news agency.
Witnesses said Shakhuri had been taken to the military hospital in nearby Dhahran with bullet wounds to his back and neck.
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The demonstrators carried posters of Shiite detainees, including prominent cleric Nimr al-Nimr, who was arrested earlier this month, witnesses said.
In recent days, confrontations have intensified between police and protesters from the kingdom's marginalised Shiite minority -- estimated at about two million and mostly concentrated in the oil-rich Eastern Province.
Two Shiite protesters were killed earlier this month, triggering attacks on government buildings in Qatif.
The district witnessed a spate of protests after an outbreak of violence between Shiite pilgrims and religious police in the Muslim holy city of Medina in February last year.
The protests escalated when the kingdom led a force of Gulf troops into neighbouring Bahrain the following month to help crush a Shiite-led uprising against the Sunni monarchy.
Meanwhile, the family of Nimr said the cleric had been transferred from the military hospital in Dhahran, where he was receiving treatment for a bullet wound, to another in the capital.
And Shiite writer Nazir al-Majed, who was arrested in March last year for taking part in protests, was released on Thursday, relatives said, adding that he was never charged or put on trial.