Two Saudi security officers and two people they were trying to detain were killed in a gunfight on Thursday in the eastern town of al-Awamiya, the government said, an area where minority Shi'ite Muslims have staged regular anti-government protests.
Shi'ites in the region complain of discrimination, a charge denied by Sunni Muslim-ruled Saudi Arabia, the world's largest oil exporter, and the Riyadh government blames Shi'ite-led neighbour Iran for the rise in tensions.
Saudi opposition activists said security forces stormed a home in Awamiya belonging to the brother of a man on a list of 23 people wanted by the authorities over unrest, before shooting dead two unarmed men they found inside.
They said one of the two was the house owner's 22-year-old son and the other a prominent local photographer known for documenting demonstrations and protester funerals that had taken place in the area over the past three years.
The wanted man was not in the house at the time, they said.
An Interior Ministry spokesman said security forces came under fire while trying to arrest "a number of armed troublemakers" who had previously fired on residents and security forces in Awamiya, according to state news agency SPA.
It said the security forces responded to the source of shooting in accordance with standing rules.
"As a result of the exchange of fire, the wanted men Ali Ahmed al-Faraj and Hussein Ali Madan al-Faraj were killed," SPA said, adding that two security men had also died and two more were wounded.
It said two pieces of weapons, a bullet-proof vest, a pair of binoculars used by snipers and a large amount of ammunition were found at the scene.
Local activists denied that there was any exchange of fire at the scene and said security forces burst into the house of a man in search of his wanted brother who was not there.
They said that Ali, the house owner's son, was shot 11 times while trying to run away. The second man, Hussein, died "as he documented the raid," one activist told Reuters.
On Wednesday, a Riyadh court sentenced seven men to between six and 20 years in jail for offences that included taking part in protests in the town of Qatif, in Saudi Arabia's Eastern Province, state news agency SPA said.
SPA said the seven had been also convicted of chanting slogans against the kingdom as well as possessing and making petrol bombs and hurling them at security forces.
Minority Shi'ites have staged sporadic protests in Qatif since 1979. The town's most recent wave of demonstrations began during the Arab uprisings of 2011 and continued through 2012.
At least 20 people were killed as Shi'ite youths took to the streets to demand equal treatment in the Sunni-ruled kingdom.
Shi'ites accuse Saudi authorities of persistent discrimination against them and say some protesters were shot.
Saudi Arabia, a US ally and the world's top oil exporter, denies discriminating against Shi'ites and says all the killings resulted from exchanges of gunfire when police were attacked.
In 2012, Saudi Arabia ordered the arrest of 23 Shi'ites in the oil-producing Eastern Province, where many of the kingdom's Shi'ites live, saying they were responsible for unrest.
Saudi media have said only nine of the 23 remain at large. The rest have been captured, killed or turned themselves in.
Saudi Arabia recently ratified an anti-terrorism law that rights activists have condemned as a tool to stifle dissent.
REUTERS