The Vietnamese government has stripped a French-Vietnamese and mathematics lecturer and former political prisoner of his Vietnamese citizenship.

According to the AFP news agency, 62-year-old Pham Minh Hoang was a dual citizen.

In 2011, he was sentenced to three years in jail for attempted subversion but was released after 17 months and ordered to serve three years’ house arrest.

Phạm was convicted for writing a series of articles under the pen name Phan Kiến Quốc.

Prosecutors say his writing tarnished the country’s image and was aimed at overthrowing the government.

In May, Hoang received a letter signed by President Trần Đại Quang, informing him of the Vietnamese government’s official decision to revoke his nationality.

Revoking Hoang’s citizenship effectively renders his status illegal in Vietnam.