Malaysian police said Sunday they have discovered mass graves in more than a dozen abandoned camps used by human traffickers on the border with Thailand, where Rohingya Muslims fleeing Myanmar have been held.

“These graves are believed to be a part of human trafficking activities involving migrants,” Home Minister Zahid Hamidi told reporters.

He did not say how many bodies have been recovered.

Similar camps and dozens of remains were recovered in jungle camps across the border in Thailand earlier this month, where Rohingya fleeing persecution in Myanmar had been held by traffickers and held until their families could pay for their freedom.