Indarjono said the two Thais were arrested Oct. 13 upon arrival at the airport with a total of 958 grams (33.8 ounces) of methamphetamine concealed under their clothes.
He said that three days later, customs officers nabbed the Russian woman and the Frenchman, who were picking up 22.5 grams (0.8 ounce) of cocaine at a delivery service.
Indonesia has extremely strict drug laws, and convicted smugglers are sometimes executed.
More than 150 people are currently on death row, mostly for drug crimes. About one-third of them are foreigners.
In May, a Frenchman was sentenced to death on Lombok, an island next to Bali, for smuggling 3 kilograms (6.6 pounds) of ecstasy. Last Wednesday, a court in Bali sentenced two Thais to 16-year jail terms for smuggling 2.2 pounds of methamphetamine.