PADANG BESAR (REUTERS) - Authorities in Thailand have dug up the bodies of six suspected Rohingya migrants from Myanmar at a rubber plantation near a mountain where a mass grave was found at the weekend, the military said on Wednesday.

The discovery was made in Thailand's Songkhla province near the country's border with Malaysia around 4km from the site where the 26 bodies were found a few days ago.

"Villagers living nearby told us the bodies buried here are the bodies of Rohingya migrants from Myanmar from nearby human trafficking camps," Colonel Jatuporn Klampasut, deputy secretary general of the Internal Security Operations Command (ISOC) Region 4, told Reuters.

Many illegal migrants in Thailand are Rohingya Muslims from western Myanmar and from Bangladesh who brave often perilous journeys by sea to escape religious and ethnic persecution.

Thousands arrive in predominantly Buddhist Thailand every year, brought by smugglers. Many are then taken into the jungle where traffickers demand a ransom to smuggle them south across the border to mainly Muslim Malaysia.

Authorities on Tuesday said they had found a second abandoned camp used for human trafficking. Three people were rescued from near the camp, Thai police said.

The United States, which has censured Thailand for failing to act against human trafficking, has called for a speedy and credible inquiry into the discovery of the mass grave.

Police in Thailand have arrested four men - three Thais and a Burmese national - on suspicion of human trafficking. Arrest warrants have been issued for a further four who are on the run.

A police officer based in Padang Besar, who spoke on condition of anonymity, said that police intelligence showed there could be three more camps on the same mountain range.

"There are three camps on that mountain with up to 700 people in each camp we are told," said the officer. "It is just a matter of time now whether we can find them as we've been told the human traffickers are being tipped off and are moving their camps."