PADANG BESAR, Thailand (Reuters) - Authorities in Thailand have dug up the bodies of six apparent Rohingya migrants from Myanmar not far from a mass grave found at the weekend, the military said on Wednesday, and U.N. officials called for a regional effort to end human trafficking.

Security forces and rescue workers inspect at abandoned camp in a jungle in Thailand's southern Songkhla province May 5, 2015. REUTERS/Surapan Boonthanom

The discovery was made at a rubber plantation in Thailand’s Songkhla province near its border with Malaysia around 4 km (2.5 miles) from the site where the 26 bodies were found a few days previously.

“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.

The remains were of four women and two men, said Jatuporn.

The U.N. refugee agency UNHCR appealed for a joint response to human trafficking by countries in the region, including addressing the root causes that drove people to turn to smugglers in the first place.

It said hundreds of Rohingyas had reported horrific abuse by smugglers in the last year, including people dying from beatings and lack of food, but that this was the first case of mass graves being found.

“It’s distressing to hear that people who escaped difficult conditions back home have had to put their lives in the hands of ruthless smugglers, only to be killed before they could reach safety,” UNHCR regional envoy James Lynch said in a statement.

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 Thailand, a predominantly Buddhist country, every year, spirited in 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.

Asked by reporters whether there had been official complicity in trafficking humans, Deputy Prime Minister and Defence Minister Prawit Wongsuwan told reporters in Bangkok: “There must be. This is not acceptable.”

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

The United States has censured Thailand for failing to act against human trafficking and it has also called for a speedy and credible inquiry..

Prawit said the United States has praised Thailand for its transparent handling of the discovery of the mass graves and suspected human trafficking camps.

Thai police have arrested four men - three Thais and a Myanmar 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. 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.”