One person was killed and three wounded when security forces exchanged gunfire with "masked men" in Saudi Arabia's oil-rich east, the official SPA news agency reported on Friday.
Activists and witnesses said the casualties came when security forces opened fire on a Shiite demonstration in the Qatif district of the kingdom's Eastern Province.
"A security force patrol came under heavy gunfire from masked men while it was carrying out its duties in Al-Shwaika neighbourhood in the Qatif district on Thursday," SPA reported, quoting a police spokesman in the province.
Security forces "responded", prompting "an exchange of fire that left four of the rioters wounded, one of whom died before reaching hospital," it added.
Activists and witnesses said that security forces opened fire when a Shiite procession marking the birthday of the Prophet Mohammed -- a celebration forbidden in ultra-conservative Sunni Muslim Saudi Arabia -- turned into a demonstration for reform and the release of Shiite detainees.
"Munir al-Medani, 21, was wounded by a live bullet to his chest," one activist said, requesting anonymity. "He was taken to hospital where he later died of his wounds."
Signup to our newsletter and follow us on Facebook and Twitter!
A number of other protesters were also wounded, the activists and witnesses said.
Witnesses said the shooting prompted groups of young protesters to burn tyres and police to set up checkpoints across the district.
Medani's death raises to six the number of protesters killed since demonstrations erupted in the Eastern Province last March against Saudi-led military intervention to help crush Shiite-led pro-democracy protests in neighbouring Bahrain.
Activists say that Saudi authorities have arrested nearly 500 people since the protests started. Many have been released but dozens remain in custody, among them human rights activist Fadel al-Munasif and writer Nazir al-Majid.
In January, Saudi authorities published a list of 23 men wanted on suspicion of involvement in the disturbances.
Later the same month, the interior ministry announced that security forces had arrested nine people suspected of involvement in the wounding of three policemen in the Eastern Province.
Most of Saudi Arabia's estimated two million Shiites live in the province, where the vast majority of the kingdom's huge oil reserves lie. They complain of marginalisation in the Sunni-dominated kingdom.