CONCERNS are mounting about the treatment of two boatloads of would-be Rohingya and Bangladeshi refugees being trucked to the Thai border port of Ranong and for two more boatloads that have reportedly been ''helped on'' at sea.

The United Nations has asked the Thai Government for access to 158 men who came ashore in two boats on Thailand's southern Andaman coast over the weekend.

''We would like to determine if they are in need of international protection,'' said UN High Commissioner for Refugees spokesperson Andrej Mahecic, speaking from Geneva. ''We are definitely keen to gain access to these people.''

A source in Ranong said that the first group of 91 men, now being held at a local detention centre, were categorised as ''Burmese from the south'' rather than as Rohingya.

As Burmese, it would be possible for Thai authorities to repatriate the men to Burma, but as Rohingya, a stateless Muslim minority group constantly persecuted within Burma, they would be in fear of their lives and have clear-cut claim to refugee status.

A second group of 67 men who arrived on Sunday was reported to be being transferred by truck from the southern province of Satun to Ranong today.

Villagers close to Ranong, a busy port frequented by traders, said today that they had ''helped on'' two boatloads of men, one containing 66 and the other 40, on January 19. Military authorities had since told the villagers not to inform the media of this, National Channel Breaking News reported.

Several other boatloads of Rohingya may be off the Andaman coast of Thailand, according to information from Cox's Bazaar in Bangladesh, and sailing south to what they hope will be sanctuary in Muslim-majority Malaysia.

Colonel Chayawut Chansomboon, head of Immigration in Satun, confirmed that the two boatloads of men had arrived over the weekend. He said the intention was to send the men to the International Detention Centre in Bangkok, but the 1500-capacity centre was full.

''Authorities decided to send them to Ranong, where there is space for 300,'' he said. The second boatload was undergoing health checks, fingerprinting and debriefing yesterday and would be trucked to Ranong today, he said.

Ranong Immigration centre has a poor reputation for the care of would-be Rohingya refugees.

Two Rohingya teenagers died in the custody of Ranong Immigration in 2009 and others were bent double and transferred to Bangkok after several months of being squeezed into inadequate accommodation, with no sunlight or exercise. Rohingyas who arrived on that boat two years ago remain in detention, the UNHCR confirmed.

The novel definition of Rohingya as ''Burmese from the south'' may explain why, when Phuketwan called Ranong Immigration today, a spokesman said: ''We have no Rohingya here.''

The boatloads are the first to arrive in Thailand since 2009, rekindling the human rights outrage of the ''pushbacks'' by the Thai military that led to the deaths of hundreds of Rohingya. The Rohingya were towed out to international waters and cut adrift, with no power and little food.

Since then, the Royal Thai Navy is known to have ''helped on'' at least one Rohingya boat that made it to Malaysia last year.

The Rohingya boats, with passengers exposed to sun and rain, are generally without navigation aids and put to shore whenever food runs low, without being certain whether they are in Thailand or further south.