The first arrest, of 19-year-old Laotian Xi Bun, took place around 10 p.m. Sunday at the border of the province and Laos in a joint operation by border guards and police.
After interrogating Xi Bun, police arrested two others on Monday: a Vietnamese man named Ho Ven, 36, and a Lao man named A Roong Chu, 25.
Colonel Bui Duc Trung, head of the central region's task force on drug and crime prevention and control, said Tuesday that the case belonged to a major cross-border drug smuggling and transportation ring involving a "huge" amount of drugs, Vietnam News Agency reported.
Vietnam has been identified by security agencies as a key trafficking hub for narcotics despite having some of the world's toughest drug laws.
Those convicted of possessing or smuggling more than 600 grams of heroin or more than 2.5 kilograms of meth face the death penalty.
The production or sale of 100 grams of heroin or 300 grams of other illegal narcotics is also punishable by death.