Malaysian police say 139 suspected migrant grave sites have been found in 28 people-trafficking camps along the Thai border.
National police chief Khalid Abu Bakar said some of the graves, found since 11 May, may contain more than one body.
They are close to an area of Thailand where trafficking camps and dozens of shallow graves were found this month.
Thailand subsequently cracked down on the routes used by traffickers to move migrants through its territory.
The operation forced traffickers to move the migrants by sea instead. But thousands were left stranded after the traffickers abandoned them and no country would take them in.
The traffickers have been using the jungles of southern Thailand and northern Malaysia for years to smuggle people into Malaysia.