"The smuggling operation is the largest one that has been foiled through the Beirut International Airport," the source said on condition of anonymity.
Captagon is the brand name for the amphetamine phenethylline, a synthetic stimulant. The banned drug is consumed mainly in the Middle East and has reportedly been widely used by fighters in Syria.
The security source said the drugs had been packed into cases that were waiting to be loaded onto a private plane that was headed to Saudi Arabia.
The five Saudi citizens were still in the airport and would be questioned by Lebanon's customs authority, the source added.
In April 2014, security forces foiled an attempt to smuggle 15 million capsules of Captagon hidden in shipping containers full of corn from Beirut's port.
Lebanon's state news agency also reported Monday's drug bust, saying the private plane was to head to Riyadh and was carrying 40 suitcases full of Captagon.
Saudi Arabia's large royal family has had past run-ins with authorities in various countries.


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