PHNOM PENH (REUTERS) - Cambodia imprisoned 10 activists on Tuesday (Oct 26) for demonstrating in support of a prominent union leader who was jailed in August over accusations that he falsely claimed that land in the South-east Asian country had been ceded to neighbouring Vietnam.

Cambodia has for centuries fretted about territorial encroachments by Vietnam to the east and Thailand to the west.

The issue is highly emotive and many Cambodians are suspicious and resentful of both neighbours.

A court in the capital Phnom Penh sentenced the 10 activists, who had been demonstrating in support of border activist and trade unionist Rong Chhun, to 20 months in prison, a defence lawyer and a rights group said.

Last year, the government accused Rong Chhun of saying Cambodian farmers had lost land to Vietnam in a border post demarcation, and that the Vietnamese authorities had evicted Cambodian villagers.

Rong Chhun has denied making the remarks or stirring up trouble.

He was sentenced to two years in prison this August.

The activists were arrested in August and September last year, and will be placed under probation for two years upon their release, rights group Licadho said in a statement.

Their sentencing comes amid a broad crackdown in Cambodia on the opposition, civil society and the media that began in the run-up to a 2018 election.

"The trial mostly consisted of the activists being asked if they had obtained prior permission to gather, and if they had someone from outside the country encouraging or paying them to engage in the peaceful calls for Rong Chhun's release," Licadho said.

The activists were also fined US$500 (S$670) each, according to Mr Sam Chamroeun, one of the group's defence lawyers.

"I and my clients can't accept this verdict and I will discuss with them whether or not to appeal," he told Reuters.