Saudi security forces have opened fire on Shia protesters in the Qatif district of Eastern Province, wounding several of them as hundreds marched to demand the release of detainees, witnesses said.
Live rounds fired by anti-riot police injured a number of protesters who took to the streets in the early hours on Friday, 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 was on a list of 23 wanted people.
"There were no casualties," the ministry said in a statement.
Witnesses said Shakhuri had been taken to the military hospital in nearby Dhahran with bullet wounds to his back and neck.
The demonstrators carried posters of Shia detainees, including prominent cleric Nimr al-Nimr, who was arrested earlier this month, witnesses said.
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.
In recent days, confrontations have intensified between police and protesters from the kingdom's Shia minority, estimated at about two million and mostly concentrated in the oil-rich Eastern Province.
Two Shia 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 Shia pilgrims and religious police in the Muslim holy city of Medina in February last year.