No one has claimed of responsibility for the attack.
 
Asked if some of those arrested had been charged for the killing, Turki said: "Not yet, we still have to complete the investigation".
 
Security forces are looking for two more Saudi nationals, who were named as Abdallah Sayer al-Mohammadi and Nasser bin-Latif al-Balawi, the interior ministry said in a statement.
 
"We just want them to appear at the nearest police station and clear their names," Turki said.
 
Anger
 
The ministry gave the two men 24 hours to turn themselves in and offered $1.9 million for information leading to their arrest.
 
Saudi Arabia has vowed to crack down on Islamic militants and has condemned the attack.
 
Fighters swearing allegiance to al-Qaeda launched a campaign to topple the US-allied Saudi monarchy in 2003, carrying out attacks on foreigners and government installations, including the oil industry.
 
Tough security measures and a powerful publicity campaign helped crush the violence but analysts and diplomats have said the underlying drives of radical Islamic ideology and anger at Western policy in the region remain strong.