A prominent international advocacy group demanded Monday that Kazakhstan suspend the ongoing trial of 37 people accused of mounting mass riots in a western oil town last year.

New York-based Human Rights Watch said in a statement that many defendants claim they only yielded incriminating testimonies after being subjected to physical abuse while in detention.

The unrest in Zhanaozen in December came after a seven-month long occupation of the main square by oil workers demanding higher salaries. A confrontation with police descended into rioting during which at least 16 people were killed.

A number of police officers are expected to go on trial for deploying live rounds against rioters.

The events stunned the country and exposed seething social tensions in the otherwise stable oil-rich Central Asian nation bordering China and Russia, prompting international concern.

Authorities argue that the Zhanaozen disturbances were organized by individuals seeking to sow political instability.

HRW says defendants were beaten and ill-treated into giving statements incriminating themselves and others.

"Torture is a serious crime. The defendants' allegations need to be investigated and anyone responsible brought to account," said Mihra Rittmann, a Central Asia researcher at HRW.

One person detained by police and held in custody for two days died several days later in hospital from injuries apparently sustained in custody, the group said.

Interior Ministry officials have previously denied all claims that participants in the disorder in Zhanaozen were mistreated.

Allegations of physical abuse will raise doubts about the prospects for a fair trial. Hearings began last month and some defendants are being tried for charges that could see them receiving jail terms of up to 10 years.

Kazakhstan is an increasingly important source of oil and gas, as well as uranium, zinc and copper. The Northern Distribution Network that supplies U.S. and coalition forces in Afghanistan goes through the former Soviet republic's vast steppe territory.