Malaysian authorities have found mass graves containing the remains of more than 20 people believed to be human trafficking victims near the border with Thailand, police said on Sunday.

The heavily forested Thai-Malaysian border has been a transit point for smugglers bringing people to Southeast Asia by boat from Burma and Bangladesh.

The migrants are often held for ransom in squalid detention camps and according to some accounts face torture and starvation.

Police uncovered 24 bodies on Saturday in the Bukit Wang Burma area near the Malaysian border with Thailand, close to where authorities in May had found hundreds of bodies in illegal detention camps.

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“Following on from the operation in which we found … bodies of illegal immigrants, 24 more bodies have been found and dug up,” police said in a statement, adding that the remains had been handed over to medical experts.

It was not immediately clear if the bodies discovered were those of Rohingya, a minority ethnic group in Burma, whose members have fled widespread persecution in that country.

A crackdown by Thai authorities in May drove traffickers to abandon thousands of migrants on rickety, overcrowded boats in Southeast Asian waters, triggering a regional humanitarian crisis that saw them land in Malaysia and Indonesia after being rescued by fishermen.