Prosecutors in Thailand have called their first witnesses in a major human trafficking trial with 92 defendants, including a senior army officer, implicated in smuggling, kidnappings and the deaths of dozens of people.

The case came to light after more than 30 bodies were discovered last year in shallow graves in southern Thailand, exposing networks that trafficked Rohingya Muslims fleeing persecution in Myanmar and held them for ransom in jungle camps.

Human rights groups have long accused Thai authorities of collusion in the trafficking, but officials routinely denied the claims.

Several high-ranking officials have been charged in the case, including army officers, police and local politicians. The 92 defendants face human trafficking and a variety of other charges. All have pleaded not guilty.