The attempted attack at the Tan Son Nhat airport in Ho Chi Minh City in April caused a scare but no casualties.
The communist government linked it to the Provisional Central Government of Vietnam, or PCGV, an exile group established in 1991 and little known locally but tied to the defeated US-backed South Vietnamese republic.
A court in Ho Chi Minh City in December convicted the group's local members of terrorism and sentenced them up to 16 years in jail.
The Ministry of Public Security said in a statement today the group is a terrorist organisation and those associated with it including joining, instigating others to join, sponsoring or receiving assistance from the group, attending the group's training courses will constitute terrorist offense and will be dealt with in accordance with law.
Another group, the California-based Vietnam Reform Party or Viet Tan, was declared a terrorist organisation in 2016 and was accused of sending arms and planning attacks.
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