Less than two weeks after Malaysia declared that it had no migrant "death camps" on its soil, the country's police have discovered several mass burial sites near the border with Thailand, a revelation that further underscores the horrors that face those fleeing violence and persecution in their home countries.

Malaysian Home Minister Zahid Hamidi said on Sunday police were working to glean more details from "mass graves that were found" amongst 28 camps used, and abandoned, by human traffickers. Local media reported the discovery of roughly 100 bodies in a single grave, adding to at least 33 discovered by Thai police earlier in the month. Malaysia has uncovered 139 graves in the northern state of Perlis, Malaysian authorities said.

"We don't know how many [bodies] there are. We are probably going to find more bodies," Mr. Hamidi told reporters.

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Many of the dead are suspected to be Rohingya, a Muslim minority persecuted and barred from citizenship in Myanmar. At least 140,000 Rohingya are in refugee camps inside Myanmar, and up to 100,000 more have fled in a tide of desperation, the scale of which has not been seen since hundreds of thousands of migrants left Vietnam in the 1970s and 1980s.

But in placing themselves in the hands of human traffickers, Rohingya have exposed themselves to abuses the magnitude of which have seized global attention in recent weeks after thousands of migrants were left floating on boats, some for months with little food and water, as neighbouring countries barred them from coming to land.

The coincident discovery of mass graves further underscores the perilous conditions for the 1.3-million Rohingya who rank among the most-persecuted minorities on earth, but whose plight has garnered only sporadic international attention.

For many, the search for better fortunes often includes time spent in jungle camps run by smugglers holding human cargo in part to extort money before bringing them to their destination. Rohingya who have transited the camps say smugglers beat them and routinely threaten their lives in order to compel relatives to transfer more cash. Death is a constant companion of the illegal trade in humans, with terrible conditions that cause some to fall ill or starve to death, and criminal operators with a cavalier attitude toward the lives of those whose money they take.

The discovery of the graves on Thai and Malaysian soil also highlights the complicity of authorities in those countries that often turn a blind eye – or actively profit from – the movement of people through their territories. Malaysia said the recently discovered camps had been there for at least five years.

"These camps are in fact surrounded by local officials and communities taking money from the traffickers and at more senior levels, say at the provincial level, we have officials looking the other way," Phil Robertson, deputy director of Human Rights Watch in Asia, said earlier this month.

In Thailand, some local communities have grown so frustrated by official inaction that they have formed their own militias in an effort to drive away traffickers.

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The heightened attention to the issue in recent weeks has prompted governments in Thailand and Malaysia to respond more assertively, and Thailand has begun trying to root out police involved in trafficking.

Malaysia and Indonesia have also offered to shelter migrants fleeing by sea for up to a year, after 3,600 landed on their shores since May 10 alone. Both countries have also mounted search-and-rescue patrols, amid international condemnation of inaction among Myanmar's neighbours.