A Cambodian court has begun hearing the appeal of a radio station owner who claims his 20-year prison sentence on insurrection charges was the result of a political vendetta by the government.

The lawyer defending 71-year-old Mam Sonando, Sar Sovan, said Tuesday that the Appeals Court hearing was expected to last three days.

Mam Sonando's Beehive Radio is one of the country's few radio stations broadcasting criticism of Prime Minister Hun Sen's government. Human rights groups say his conviction was unsupported by evidence and are seeking his release.

The Phnom Penh Municipal Court convicted Mam Sonando last October on four insurrection and rebellion counts on the basis of his alleged links to a secessionist movement in eastern Cambodia blamed for a violent conflict over land-grabbing. He denies any involvement.