Saudi officials say police have arrested a number of suspects over last week's killing of four French citizens.
Interior ministry spokesman Mansour Turki would not say how many people had been detained, or whether the attack was politically motivated.
The suspects were being interrogated, he said, but it was too early to say if they belonged to any militant group.
The French nationals were travelling in north-west Saudi Arabia when gunmen opened fire on their vehicle.
Mr Turki said police were looking for two other suspects.
Saudi Arabia has being fighting Islamic militants over the past three years, during which time there have been a number of high-profile attacks on foreign nationals.
The French foreign ministry said two of the victims were employees of the electrical equipment manufacturer Schneider Electric and a third was a teacher. A fourth person, a teenager, died from his wounds the following day.
The attack happened on a road leading from the city of Madain Saleh towards the Islamic holy places in Medina and Mecca.