Malaysian police said yesterday they had found 139 grave sites containing suspected remains of Rohingya and Bangladeshi migrants, as well as 28 abandoned "detention" camps capable of housing hundreds, laying bare the grim extent of the region's migrant crisis. National police chief Khalid Abu Bakar said authorities were exhuming the remains, and it remained unclear how many bodies might lie in the pits, located in a remote and hard-to-reach area of mountainous jungle along the Thai border. But the findings appeared to indicate a system of jungle camps and graves that dwarfs those found by Thai police earlier this month, a discovery that ignited regional concern about human smuggling and trafficking. The discovery also follows repeated denials by top Malaysian officials - who have long been accused by rights groups of not doing enough to address the illicit trade - that such grisly sites existed on their soil. "(Authorities) found 139 suspected graves. They are not sure how many bodies are inside each grave," Khalid told reporters in the town of Wang Kelian near the Thai border. "They also found 28 detention camps." He said authorities were now exhuming bodies and would conduct post-mortems, adding that at least one body was "badly decomposed." So far police have provided no details on what caused the deaths. The number and size of the camps suggest they may have been capable of housing hundreds of people. Khalid said the largest could hold up to 300 people; another had a capacity of 100, and the rest could hold about 20 each. By comparison, Thai police have said they found five secret jungle camps and 35 bodies so far on their side of the border. A subsequent Thai crackdown appears to have caused nervous traffickers to abandon boats carrying migrants from Bangladesh and Myanmar's oppressed Rohingya minority. Boatloads of starving migrants have since sought to reach Malaysia, Thailand and Indonesia, and rights groups say thousands more may still be at sea. Activists have previously described how smuggled Rohingya and Bangladeshis are held by people smugglers in camps before they can be sold as slaves or indentured labourers, or ransomed back to their families. After initially turning them away, Malaysia and Indonesia last week bowed to international pressure, saying they would admit boatpeople pending their repatriation or resettlement elsewhere. Prime Minister Najib Razak said yesterday he was "deeply concerned" by the discovery in the jungle. "We will find those responsible," Najib said in comments on his Facebook page. Earlier in the month he declared "Malaysia does not and will not tolerate any form of human trafficking." But the revelation is likely to focus new attention on Malaysia's record in battling a scourge that activists say is carried out by criminal syndicates, likely with the complicity of authorities. "I am sure the authorities at the border know what is going on and who are the criminals. The top authorities must be held responsible," said Aegile Fernandez of the Malaysian labour and migrant-rights group Tenaganita. "I am sure the police know who are the criminal syndicates. It is whether they have the willpower to stop it." Anti-trafficking groups say the border region near Wang Kelian is widely known to be a key transit point on a route that funnels migrants from Bangladesh and Myanmar into Malaysia and beyond. Khalid declined to answer when asked how the extensive string of camps had been built without authorities knowing. However, he earlier said the camps and graves were in rugged areas requiring hours-long hikes to reach. The US State Department's annual report on human trafficking lists Malaysia on the lowest possible Tier 3, for not fully complying with even the minimum standards.