Pham Minh Hoang, 55, was arrested on August 13, wife Le Thi Kim Oanh said.

The authorities had earlier told Hoang, a lecturer in applied mathematics at the Ho Chi Minh City Institute of Technology, that he would be arrested if he did not confess to belonging to the banned foreign-based democracy group Viet Tan, his wife said.

'In fact, my husband is not a member of Viet Tan, so we refused,' Oanh said.

Oanh said during the arrest, police had read out the text of Article 79 of Vietnam's penal code, which bars 'activities aimed at overthrowing the government.'

In letters distributed by Viet Tan's office in Washington on Tuesday, Oanh said she believed her husband's arrest was tied to his support for protests against controversial Chinese-run bauxite mines in Vietnam's Central Highlands.

She said police were also investigating 'leadership training' courses Hoang had given for some of his university students.

Authorities in communist Vietnam have arrested dozens of democracy activists and independent bloggers over the past four years, sentencing many to multi-year prison terms.

Many of those imprisoned were accused of belonging to Viet Tan, which Vietnam considers a terrorist organization.

Most had also criticized Vietnamese policy on the bauxite mines, or had advocated stronger Vietnamese opposition to China regarding the Spratly and Paracel Islands in the South China Sea, which both countries claim.

Deutsche Presse Agentur - August 16, 2010