BANGKOK - THAILAND'S new premier must ensure that troops who tortured and killed a Muslim cleric in the far south face justice, a rights group said on Thursday, adding that such abuses fuelled unrest in the region.

Imam Yapa Koseng, a 56-year-old religious leader, was arrested in March last year and died days later in military custody in the Muslim-majority deep south, where a deadly separatist insurgency is raging.

'Prosecuting the soldiers who killed an imam in army detention will be a test of the administration of Thailand's new prime minister, Abhisit Vejjajiva,' New York-based Human Rights Watch (HRW) said in a statement.

Mr Abhisit was elected by parliament on Dec 15, and has vowed to quell the five-year long rebellion, which has left more than 3,500 people dead.

An inquest in Narathiwat province last month ruled that Yapa died after beatings by soldiers during interrogation, an army spokesman told AFP, adding that they planned to begin the process to prosecute five soldiers.

HRW said the imam's death highlighted broader human rights violations in the south, including illegal and arbitrary detention and torture including beatings, electric shocks and strangulation.

'The new government needs to overhaul the counter-insurgency strategy that encourages abuses, impose effective civilian control over the army, and provide efficient redress for victims of abuses,' said HRW Asia Director Brad Adams.

'By relying on repressive measures and restrictions on fundamental human rights, Thai authorities have created a fertile ground for the insurgency to expand.'

The southern region was once an autonomous Malay sultanate until Buddhist Thailand annexed it a century ago, provoking decades of tension. Successive governments have failed to curb the unrest. -- AFP