Saudi Arabia said on Sunday it had arrested eight suspects linked to recent clashes between militants and security forces and the booby-trapping of cars.
Security forces also seized three vehicles packed with thousands of kilograms (pounds) of explosives, including one they had been searching for since February, an interior ministry official said, quoted by the state SPA news agency.
"Eight people linked with these incidents have been captured, but the investigation requires not revealing their identities and the roles they played," the official said.
Authorities had already announced on Saturday that the car packed with explosives they had been looking for since February had been found in an eastern district of Riyadh and defused.
The interior ministry official said Sunday the 1991 GMC Suburban had been rigged with 1,300 kilograms (2,860 pounds) of explosives. The militants made changes to the vehicle, including using a fake license plate, in a bid to camouflage it.
The two other cars were packed with a total of 2,827 kilograms (6,219 pounds) of highly explosive material, the official said.
A series of suicide bombings targeting residential compounds killed 52 people in Riyadh in May and November 2003. The attacks were blamed on suspected sympathisers of Saudi-born Osama bin Laden's al Qaeda network.