Pham Minh Hoang, 62, who has dual nationality, was sentenced to three years in jail for attempted subversion in 2011, but was released after 17 months and ordered to serve three years' house arrest.

He was convicted for writing a series of articles under the pen name Phan Kien Quoc that prosecutors said tarnished the country's image and were aimed at overthrowing the government.

Hoang told AFP he had continued to publish "peaceful" articles on social media that were critical of the government since his release from prison.

He received a copy of the stamped letter from President Tran Dai Quang confirming the "removal of Vietnamese citizenship", according to the document dated May 17.

Revoking his citizenship effectively renders his status illegal in Vietnam.

According to the letter, the decision was based on article 88 of the criminal code, which criminalises propaganda against the state, and article 91, which outlaws moving abroad with a view to oppose the government.

"I am very upset and I'm waiting, I'm waiting to be expelled," an emotional Hoang told AFP over the phone Sunday.

He said he received a copy of the letter on Saturday, and was surprised not to find a clear explanation for the decision.

"I am living in a country that is very unlawful, they can do anything," he said.

Vietnamese officials did not respond to a request for comment on the issue.

Hoang vowed to appeal the decision, and has sent a letter to the French embassy in Vietnam expressing his wish to revoke his French nationality, which he hopes could force the Vietnamese government to reverse its decision.

The French embassy in Hanoi declined to comment.

Hoang said he must stay in Vietnam to care for his disabled older brother and his wife's elderly mother.

He went to France in 1973 but returned after 27 years to settle in Vietnam, where he worked as a mathematics lecturer at the Polytechnic University of Ho Chi Minh City.

He is the only dissident to have his citizenship revoked in modern memory.

Authoritarian Vietnam routinely jails bloggers, lawyers and activists accused of anti-government activity.

All media in the communist country are state-owned, but many dissidents have moved onto social media platforms in recent years to air criticism.

Agence France Presse - June 11, 2017