Malaysian authorities said on Monday they have discovered 139 suspected graves in a series of abandoned camps used by human traffickers on the border with Thailand.
The camps are where Rohingya Muslims fleeing Myanmar were believed to have been held.
Many had developed a disease called Beriberi after being captive for several months.
Chief of Mission in Thailand for the International Organisation for Migration (IOM) Jeffrey Labovitz said that he believed many of the bodies recovered in the border camps were people who became sick and were unable to continue the journey to Malaysia.
Labovitz said the migrants developed a disease called Beriberi after being captive for several months and deprived of food in the forest camps along the smuggling route between the Thai and Malaysian borders.
Thousands of migrants have landed on boats in Malaysia and Indonesia this month after Thailand cracked down on trafficking.
Thousands more are believed still at sea stranded on overcrowded boats the UN have described as “floating coffins.”