The Vietnamese government has confirmed that the pastor of a banned Protestant church has been arrested in Ho Chi Minh City.
However, the government denies the detention of the general secretary of the Mennonite Church, Nguyen Hong Quang, is connected to his religious activities.
A foreign ministry spokesman, Le Dung, says Mr Quang was arrested for his acts against public officials.
The AFP news agency earlier quoted religious sources as saying Mr Quang was detained on Tuesday after around 30 uniformed police surrounded his house in Ho Chi Minh City.
All churches and religious organisations not approved by Vietnam's ruling Communist Party are illegal.
A recent US State Department report grouped Vietnam in a worst offenders category of totalitarian and authoritarian states that view religious groups as "enemies of the state".