A Saudi policeman and an armed protester were killed in overnight clashes in the kingdom's oil-rich Shia-populated Eastern Province, the interior ministry announced on Saturday.
"A security patrol came under heavy gunfire from four armed rioters on motorbikes" in the Shia district of Qatif, ministry spokesman Mansur al-Turki was quoted by official news agency SPA as saying.
Policeman Hussein Zabani was killed while another, Saad al-Shummari, was wounded and hospitalized, he said.
"Security forces hunted down the armed rioters who were on motorbikes and exchanged fire with them," he said. "One of the four caught was wounded and he died while on the way to the hospital."
Witnesses said the attackers were participating in a protest that took place in Qatif late on Friday.
Two Shia protesters were killed earlier this month, triggering attacks on government buildings in Qatif.
Saudi Arabia is an overwhelmingly Sunni country, but Eastern Province, home to much of the country's massive oil wealth, has a large Shia minority.
Qatif witnessed a spate of demonstrations after an outbreak of violence between Shia pilgrims and religious police in the Muslim holy city of Medina in February 2011.
The protests escalated when the kingdom led a force of Gulf troops into neighboring Bahrain the following month to help crush a Shia-led uprising against the Sunni monarchy.
