Police in the northern mountainous province of Dien Bien arrested two Laotian nationals in possession of 3.5 kilograms of heroin on Sunday.
Vang A Chua, 23, and Thao So Po, 29, both resisted arrest and fought back at police with knives until they were finally captured, VietnamPlus reported.
Further investigations are under way.
Vietnam has 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 methamphetamine 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.
Although the laws are strictly enforced, drug running continues in border areas.
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