HANOI, Vietnam — Vietnam declared a California-based exile group a terrorist organization Wednesday a month after 15 local members were convicted in a failed bombing of the country’s largest airport.

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 U.S-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. Police have also issued arrest warrants for a U.S. citizen, Dao Minh Quan, the self-claimed prime minister of PCGV, and Lisa Pham, a senior member of the group, for their alleged roles in the case.

Attempts to reach both by phone in the United States were not successful Tuesday evening.

The Ministry of Public Security said in a statement Wednesday that the group is a terrorist organization 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 organization in 2016 and was accused of sending arms and planning attacks.