Malaysian police have discovered 28 camps and 139 grave sites near the country's northern border. The camps are reportedly used for human trafficking, and investigators believe that some of the graves contain more than one body, making the number of bodies difficult to tell at this time.

The camps' location is not far from the site in Thailand where similar camps and mass graves were found in early May.

Authorities believe that the camps were used for Rohingya migrants, a highly persecuted group of people from Myanmar, and Bangladeshis leaving Myanmar to find work in Malaysia, who are being held for human trafficking.

"It's a very sad scene. To us, even one [site] is serious," National police Chief Khalid Abu Bakar said, The Guardian reported. However, he did not confirm if the dead bodies were indeed Rohingya migrants.

He said the camps "have been there for quite some time. I suspect the camps have been operating for at least five years," according to MSN.

The police chief said the biggest camp was large enough to hold 300 people while the smallest one was large enough to hold 100 people, revealing the enormity of human trafficking activity going on in the area. The investigators fears that more dead bodies will be found.

Police found makeshift tents made of wood and covered by tarpaulin where the migrants were possibly held. One of the sites discovered could have been vacated no more than two weeks because police saw food supplies and cooked meals in the premises.

The thick forest area along the border of northern Malaysia and Thailand has been identified as a smuggling route used to smuggle people by boat from Myanmar to other parts of southeast Asia. Most of the victims are Rohingya Muslims and Bangladeshis.

According to migration researchers, human traffickers taking people out of Myanmar and Bangladesh would hold them in camps while they negotiate with their families for payment. The victims are given harsh treatment and are often malnourished. They are typically beaten in order to pressure their families to give more money.

"When they initially get on the ship from Myanmar, they think $200 is the cost all the way to Malaysia," explained Amy Smith, executive director of human rights organization Fortify Rights. They are then taken, to their surprise, to a remote camp in the forest where an armed guard watches over them, the New York Times reported.

The victims are ordered to call their families. The smugglers beat them while they are on the phone so their family will be forced to give $1,000 to $2,000 for their release.

Malaysian Prime Minister Najib Razak tweeted that he is "deeply concerned with graves found on Malaysian soil purportedly connected to people smuggling." He added, "We will find those responsible," according to the New York Times.