The 139 graves uncovered near people-smuggling camps in northern Malaysia appear to hold only one body each, Malaysia's deputy home minister said on Thursday, after earlier suspicions that they could contain multiple corpses of trafficked migrants.

"There is no mass grave. This is one person, one grave," Wan Junaidi Tuanku Jaafar told reporters at a news conference near the sites, adding that the bodies had been buried with "proper white wrapping" and ceremonial camphor had been used.

"The reason for the exhumation is to see whether a crime has been committed, violence was made against those people."

Four bodies have so far been recovered since Malaysian police forensic teams began digging this week at abandoned jungle camps along the Malaysia-Thailand border. Wan Junaidi said the task should be completed by the first week of June.

The dense forests of southern Thailand and northern Malaysia have been a major stop-off point for smugglers bringing people to Southeast Asia by boat from Myanmar, most of them Rohingya Muslims who say they are fleeing persecution, and Bangladesh.

The grisly discoveries in Malaysia followed the uncovering of similar graves on the Thai side of the border in early May, and the scale of the finds has raised questions about the level of official complicity on both sides of the border.

Wan Junaidi had said on Wednesday that 12 Malaysian police officials had been detained as a result, but on Thursday clarified that only two were directly connected with the discovery of the graves near the border village of Wang Kelian.

"Actually, two of them are suspects connected to the graves at Wang Kelian," the minister said. "The remainder are connected to human trafficking and to the operation we started in 2014. No connection to the graves.

He said the two police officers were suspected of involvement in transporting the migrants, but did not elaborate.

Thailand launched a crackdown on the camps - where migrants were typically held until a ransom was paid - after finding at least 36 bodies on its side of the border in early May, after which traffickers abandoned thousands of migrants in overloaded boats in the Bay of Bengal and Andaman Sea.

More than 2,500 migrants could still be stranded at sea, according to estimates by the United Nations.

Representatives from 17 countries from the Association of Southeast Asian Nations (Asean) and elsewhere in Asia, along with the United States, Switzerland and international organisations, will meet in Thailand on Friday to discuss how to tackle the migrant crisis.

"This is an international problem," said Wan Junaidi. "The migrants hail from both Myanmar and Bangladesh ... This is not a Malaysian problem alone. It's an Asean problem."