Police in Malaysia say they have discovered 139 grave sites in abandoned camps close to the Thai border.
The country's police chief Khalid Abu Bakar said some of the graves may contain more than one body.
The graves were found at 28 suspected human trafficking camps just 500 metres from the border in northern Malaysia.
"It's a very sad scene... To us even one is serious and we have found 139," Mr Bakar told reporters.
"We are working closely with our counterparts in Thailand. We will find the people who did this."
The find comes just weeks after dozens of bodies were found in shallow graves across the Thai border.
Officials said they had also found signs of torture used at the camps.
Mass graves and the site of a suspected human trafficking camp have been discovered by Malaysian police in towns and villages bordering Thailand, a senior minister has said.
Home Minister Ahmad Zahid Hamidi said officials are determining whether the graves were of human trafficking victims, but did not say how many dead bodies were discovered.
"This is still under investigation," he told reporters at the sidelines of an event in Kuala Lumpur.
According to media reports, the mass graves were believed to contain bodies of hundreds of migrants from Myanmar and Bangladesh.
Malaysia's prime minister says his country will conduct search and rescue operations for thousands of stranded migrants.
More than 3,000 people, including Rohingya Muslims fleeing persecution in Burma and Bangladeshis trying to escape poverty, have arrived in overcrowded boats on the shores of Indonesia, Malaysia and Thailand.
Najib Razak tweeted that he had ordered his country's navy and coastguard "to conduct search and rescue efforts (for) Rohingya boats. We have to prevent loss of life".
Malaysia and Indonesia have said they will provide temporary shelter to migrants, but have appealed to the international community for help in resettling them.
Indonesia and Malaysia will provide temporary shelter to thousands of migrants who had been stranded at sea, marking the first breakthrough in the humanitarian crisis confronting south-east Asia.
Most of the migrants are the persecuted Rohingya Muslim minority from Burma and others are Bangladeshis fleeing poverty.
The agreement came as more than 430 migrants who had been stranded at sea for months were rescued and taken to Indonesia.
"Indonesia and Malaysia agreed to continue to provide humanitarian assistance to those 7,000 irregular migrants at sea," Mr Anifah told reporters.
He said the two countries "also agreed to provide them temporary shelter provided that the resettlement and repatriation process will be done in one year by the international community".
Hundreds of Rohingya and Bangladeshi migrants have been brought to shore in Indonesia's northwestern Aceh province, Reuters reported, citing a search and rescue official.
"In total we found around 500 people out at sea and they are being brought to land in smaller boats," Khairul Nova, of the national search and rescue agency, said.
Over 350 migrants have been brought to shore by local fishermen in the town of Kuta Binje and are being registered by immigration authorities, a witness told the news agency.
The latest group brought to shore adds to the over 2,000 who have managed to land in Indonesia and Malaysia after weeks of drifting in the Andaman Sea with little food or water.
More than 100 migrants have been brought to shore by fishermen in Indonesia's northwestern Aceh province, Reuters reported, citing a search and rescue official.
"Nearly 400 more have been sighted at sea and fishermen are attempting to bring them to land," Khairul Nova, of the national search and rescue agency, said.
Nova said the Rohingya and Bangladeshi migrants had landed in the town of Kuta Binje in Aceh.
The latest group brought to shore adds to the nearly 1,400 who have managed to land in Indonesia after weeks of drifting in the Andaman Sea with little food or water.
More than 700 migrants who were stranded on a boat in south-east Asian seas after being turned away by Thailand and Malaysia have been rescued.
The migrants from Myanmar and Bangladesh were brought ashore to the east coast of Aceh on Indonesia's island of Sumatra this morning, a search and rescue official said.
"The latest information we have is about 794 people were found in the middle of the sea and brought ashore by fishermen at 5am," Khairul Nova, the official in the town of Langsa in Aceh, said.
"They are now in a warehouse by the port as a temporary arrangement," Nova added.
Thousands of migrants are stranded on similar boats in Southeast Asian seas as governments in the region seek to prevent them from landing, despite a UN request to rescue them.
Crisis erupts as Thailand refuses entry to 300 Rohingya migrants found drifting on an abandoned boat in its waters.Read the full story ›
Relatives of the passengers who went missing when Malaysia Airlines flight MH370 disappeared last year have demanded answers over what happened to the doomed plane.
Family members of the missing gathered outside the Malaysian Embassy in Beijing today, on the one year anniversary of the plane's disappearance, waving banners saying "Never give up. Search on" and "MH370. Tell us truth."
An interim report into the missing Malaysia Airlines flight MH370 says an underwater locator beacon battery had expired a year before the plane disappeared.