Updated

Vietnamese police have arrested four activists accused of attempted subversion as the communist authorities show no tolerance of dissent.

The Ministry of Public Security said in a statement on its website that the four were taken into custody on Sunday.

The four had been jailed for anti-state convictions previously.

They were connected to lawyer Nguyen Van Dai who was arrested along with activist Le Thu Ha in December 2015.

Despite sweeping economic reforms launched three decades ago, Vietnamese authorities maintain tight control on society and the media and tolerate no challenges to the Communist Party's monopoly on power.

Their arrests came a month after the two activists were given harsh sentences for anti-state propaganda.