Two Indians and a Saudi policeman were wounded by gunfire in the east of the kingdom as authorities hunted suspects linked to unrest by minority Shias, the interior ministry said on Tuesday.
A police traffic patrol "came under heavy fire from a farming area" in the Shia-populated Qatif district on Monday evening, the ministry's spokesman said.
The Indians were passers-by, he said, adding that they were in stable condition in hospital.
An official at the Indian embassy did not immediately have details of the incident.
The ministry spokesman did not identify the perpetrators but warned the public not to provide assistance to people on a list of 23 wanted suspects issued in 2011 after Shia unrest.
Saudi Arabia's Shia minority, who complain of marginalisation in the Sunni-dominated kingdom, began protests that year in Eastern Province, where most of them live.
Many suspects on the wanted list have already been detained or killed in shootouts.
Last month, Saudi Arabia's Supreme Court confirmed a death sentence against Shia cleric Nimr al-Nimr, a leader of anti-government protests convicted of sedition and other crimes.
Activists are calling for the sentence not to be carried out, saying Nimr engaged only in peaceful opposition.
He is one of seven Shias sentenced to death in connection with Shia unrest since 2011, activists say. Three of the convicts were under the age of 18 at the time of their arrests.
Over the past year, Saudi Shias have been targeted by suicide bombings and shootings claimed by the Islamic State group, which considers them heretics.
In the latest attack, a gunman killed five Shias in the Qatif area last month during commemorations of Ashura, one of the holiest observances of their faith.