Police in Thailand found at least 32 graves believed to belong to migrants from Myanmar who died from disease or starvation on Friday in remote jungle in Thailand's south.
The site is in an area criss-crossed with people smuggling routes in Songkhla province, at an abandoned camp. Officials say the "boat people" had apparently been trafficked to Thailand's border with Malaysia.
Migrants, many of them Rohingya Muslims from western Myanmar and from Bangladesh, brave often perilous journeys by sea to escape religious and ethnic persecution and to seek jobs in Malaysia and Thailand, a regional human trafficking hub.
Four bodies had been exhumed so far, said Police Colonel Anuchon Chamat, deputy commander of Nakorn Si Thammarat Provincial Police. A total of at least 32 graves were found in a "well set up" smuggling camp.
"The bodies were all decayed," rescue worker Sathit Thamsuwan said, adding a single man from Bangladesh survived and was being treated at a hospital in nearby Padang Besar.
The graves are the first discovery of its kind in Thailand.
The discovery highlights the brutal nature of the trafficking trade in which hundreds are believed to have died in camps or at sea.
Every year, thousands of Rohingya and Bangladeshi boat people arrive in Thailand, brought by smugglers. Many are taken by road to camps in the jungle, where traffickers demand a ransom to smuggle them south across the border to Malaysia.
Thousands of Rohingya, described by the UN as one of the world's most persecuted minorities, have fled deadly communal unrest in western Rakhine state since 2012.
Thailand has been criticised in the past for pushing boatloads of Rohingya entering Thai waters back out to sea and for holding migrants in overcrowded facilities.
The US State Department, which last year downgraded both Thailand and Malaysia to Tier 3, the lowest rank on its Trafficking in Persons scale, is currently considering pleas for Thailand to be lifted back up to Tier 2.