As world leaders gather in Phnom Penh for the ASEAN Summit and East Asia Summit, they should be aware they have arrived in a country that has a darker side – despite the sheen of progress.

The guest list includes Indian Prime Minister Manmohan Singh, Japan’s Prime Minister, Yoshihiko Noda, Australian Prime Minister Julia Gillard and Barack Obama, the first sitting US president to visit Cambodia.

The Cambodian government will want to use the summits to boost its international reputation and showcase its gains in bringing about relative stability, economic growth and poverty reduction.

But not too far from where the leaders will gather is Prey Sar Prison, where Mam Sonando, a 71-year-old journalist and human-rights defender, is serving 20 years after being convicted for anti-state crimes on trumped-up charges.

Amnesty International considers Sonando to be a prisoner of conscience, jailed solely for the peaceful exercise of his right to freedom of expression.

Sonando’s case symbolises a disturbing deterioration in Cambodia’s human-rights situation: a crackdown on freedom of expression amid widespread conflicts over land ownership and forced evictions.

One of the root causes of these conflicts is the granting of economic land concessions, which the government has handed to businesses for industrial agricultural exploitation without meaningful consultation with the affected communities.

The government has announced a moratorium on such concessions, although there is doubt that this is being properly implemented.

On October 1, Mam Sonando began his two-decade prison term, having been tried and found guilty for instigating “insurrection” in Kratie province’s Pro Ma village.

Amnesty International monitored the trial. No evidence was presented that any insurrection occurred, or that Sonando was involved.

Sonando owns Beehive Radio, one of the  few independent radio stations in Cambodia that give air time to opposition politicians.

His shocking conviction seems to be nothing more than an attempt by Cambodian authorities to cover up a land dispute and violent forced eviction, with the benefit of gagging a long-time government critic.

Pro Ma villagers, whom Sonando supposedly encouraged to secede from Cambodia, had been involved in a long-running dispute with a rubber company.

The manufactured secessionist plot was used as a pretext for the violent eviction of the community in May, during which security forces shot dead a 14-year-old girl.

The following month, Prime Minister Hun Sen gave a public speech in which he implicated Sonando in the secessionist plot.

This came soon after Sonando’s radio station broadcast a report about a complaint lodged at the International Criminal Court about forced evictions in Cambodia.

The people of Pro Ma aren’t alone – they’re just one of countless communities that have been affected by land conflicts in Cambodia.

Hundreds of thousands of people have suffered. They have been driven further into poverty, and many left without homes and without access to jobs and services such as health care and education.

Communities affected by land conflict and their supporters also face harassment, arrest, legal action and, increasingly, violence for peacefully standing up for their rights.

In January this year, military personnel shot at villagers defending their farmland in Kratie province’s Snuol district.

In April, military police shot dead prominent environmental activist Chut Wutty in Koh Kong province while he was researching illegal logging that destroys the forests on which communities rely for their livelihoods.

Compounding the problem is a corrupt, politicised justice system firmly on the side of the authorities and powerful business interests.

It effectively grants impunity to perpetrators of human-rights abuses, while actively persecuting those who speak out against violations.

No one has been held accountable for the killing of the 14-year old in Pro Ma, but six other activists and villagers were convicted with Sonando over the so-called plot.

In May, 13 women from Phnom Penh’s Boeung Kak were sentenced to more than two years in prison after they had been peacefully demonstrated about the forced eviction of their community. And the wheels of injustice turn, it seems.

Last week, in a pre-summit clean-up, residents near Phnom Penh’s airport who faced eviction were arrested and detained for painting “SOS” and putting pictures of Barack Obama on their roofs to draw attention to their situation.

Meanwhile, a number of prominent activists are under judicial investigation for their peaceful activities in support of communities affected by land conflict.

Mam Sonando’s case, then, is a prism though which the main elements of Cambodia’s deteriorating human-rights situation can be viewed: land grabs and conflict resulting in forced evictions, a corresponding crackdown on the freedom of expression of those who resist and speak out, and a complicit justice system.

By demanding Sonando’s release, summit leaders would not only be supporting a human-rights defender who is wrongfully imprisoned.

They would send a signal that they care about the plight of the Cambodian people. And they would remind the Cambodian government that the world is watching, providing moral support to activists and communities who peacefully stand up for their rights.

Rupert Abbott is Amnesty International’s researcher on Cambodia, Laos and Vietnam.