BANGKOK (AFP) - The United Nations said Tuesday it had urged Thai authorities against deporting more than 200 Muslim boatpeople from Myanmar being held in southern Thailand after they were intercepted en route to Malaysia.

Thai police arrested 259 people on an island off the southern province of Ranong Saturday, days after activists reported a surge in the number of stateless Rohingya Muslims fleeing Myanmar's restive Rakhine state.

"We're seeking details from the authorities and appealing for them not to deport the group to a place where their lives or freedom could be threatened," said Vivian Tan, a spokeswoman for the UN refugee agency (UNHCR) in Bangkok.

She added that if the detainees were found to have fled persecution the UNHCR asked they be granted "temporary stay, assistance and protection in Thailand until longer-term solutions are found".

Thousands of Rohingya - a Muslim minority group not recognised as citizens in Buddhist-majority Myanmar - have fled deadly communal unrest in Rakhine since 2012. Most have headed for mainly Muslim Malaysia.

Myanmar views its population of roughly 800,000 Rohingya - described by the UN as one of the world's most persecuted minorities - as illegal immigrants from Bangladesh and denies them citizenship.

On Tuesday Ranong deputy provincial police commander Kritsak Songmulnak told AFP that officials were determining whether the detainees had entered Myanmar illegally or were victims of trafficking.

"259 Myanmar Muslims were arrested on Saturday, of these 13 are children... They said they wanted to go to Malaysia to work to earn money," he said.

"We have no policy to deport them yet," added Kritsak.

Last month Thai officials arrested 53 Rohingya migrants in southern Thailand for illegal immigration but after further investigation declared them to be victims of trafficking.

Rights groups say the stateless migrants often fall into the hands of people-traffickers.

They have also criticised Thailand in the past for pushing boatloads of Rohingya entering Thai waters back out to sea and holding migrants in overcrowded facilities.

Two weeks ago the Arakan Project, a Rohingya rights group, said around 900 people a day were making the perilous journey by sea to flee Myanmar.

Director Chris Lewa called the exodus "unprecedented", saying some 100,000 people have fled by sea from western Myanmar since June 2012, when conflict between Buddhist and Muslim communities spiralled into bloodshed across Rakhine.

The violence left 200 people dead and a further 140,000 in displacement camps, mainly Rohingya.