HANOI (AFP) - Four Buddhist activists have been jailed in Vietnam for anti-state propaganda for flying the flag of the defeated southern regime loathed by the ruling communists, state media said Wednesday (Jan 24).

The conservative leadership of the one-party state has ramped up a crackdown on dissent since 2016.

At least 24 activists were convicted last year alone, with another 28 arrested, according to Human Rights Watch.

The four men belonging to the Hoa Hao Buddhist sect were the latest to be put behind bars after one of them hung the yellow and red flag of the former US-backed South Vietnam regime on April 30, 2016, a national holiday known as Liberation Day.

The flag is a symbol of the defeated southern regime - Hanoi's bitter enemy in the long and bloody Vietnam War - and it is considered incendiary to display it.

Vuong Van Tha, 49, was jailed for 12 years for "propaganda against the state" after the one-day trial on Tuesday, reported the official newspaper of An Giang province where the men were tried.

His son was given seven years in jail and twin brothers Nguyen Van Thuong and Nguyen Nhat Truong were sentenced to six years behind bars, the newspaper added.

It was not immediately clear if the twin brothers were related to Tha.

Tha has already spent time in jail for anti-state propaganda, and was released in 2015 after serving three years.

There are several trials scheduled this month before lunar new year in mid-February, including two activists who protested against a massive toxic spill by Taiwanese steel firm Formosa.

In a report last week, Human Rights Watch said more than 100 dissidents were behind bars "simply for exercising their basic rights".

The government rejected the report as untrue.

The Buddhist-majority communist country has been accused of religious intolerance, especially against religious groups which have adopted social or political causes.

The small Hoa Hao sect has come under fire in the past for its criticism of the state.