Spokesman Major General Mansour Turki said five Saudi citizens and one Bahraini had been detained in the operation after police uncovered 22.6 million amphetamine pills hidden inside coils of barbed wire and rolls of plastic.
Drug smuggling can be punished by death in the conservative Islamic kingdom. All narcotics and alcohol are illegal in Saudi Arabia, which has a young population and applies sharia (strict Islamic law).
An investigation into the seizure of the drugs turned up a connection to an international drug smuggling ring led by a Syrian national, Turki told the state news agency SPA.
In 2010 Saudi Arabia received around 7 tons of Captagon tablets, one of the most popular forms of amphetamine in the Middle East, representing around a third of total world supply, according to the United Nations Office on Drugs and Crime.
Production of Captagon in Syria has soared over the past two years as a result of the breakdown in order caused by the country's civil war.
Riyadh is a leading supporter of rebels fighting to bring down Syrian President Bashar al-Assad, who is a major ally of the kingdom's top regional rival Iran. REUTERS