By Jonathan Head
BBC News, Bangkok
The dramatic testimony from survivors of a draconian Thai military policy of towing Rohingya boat people out to sea and leaving them there has drawn international attention to the plight of one of the world's most oppressed people.
The numbers heading out into the Andaman Sea have increased sharply
So what is it that is driving so many Rohingya, a Muslim minority from the western-most part of Burma, to flee in rickety boats in the hope of finding refuge elsewhere?
The term Rohingya refers to a distinct, Muslim ethnic group living in northern Rakhine state, along the border with Bangladesh.
They are thought to be descended from Arab and other Muslim traders who travelled and settled there more than 1,000 years ago.
They speak a dialect of Bengali similar to that spoken in the Cox's Bazaar region of Bangladesh.
There are perhaps one million living there, but may be as many more living overseas, mainly in Bangladesh, Saudi Arabia and Malaysia.
Harassed and beaten
Northern Rakhine state is one of the poorest and most isolated in Burma.
But the burdens imposed on the Rohingya by Burma's military rulers make their situation a whole lot worse than other people living in the area.
"Economic hardship and chronic poverty prevents many thousands of people in north Rakhine state from gaining food security," says Chris Kaye, the country director for the UN's World Food Programme who visited there two months ago.
"Many do not have land rights or access to farmland to grow food, and the restrictions and limitations on the movement of people, goods and commodities places additional stress on people's livelihood opportunities."
For a start, the Rohingya are denied citizenship under Burma's 1982 citizenship law, which leaves them out of the 135 ethnic groups officially recognised by the state.
The official view of the Burmese military is that they are illegal immigrants from Bangladesh or their descendants.
Rohingya trying to leave Burma are often harassed and beaten by the Burmese security forces, but then allowed to leave, and told never to return.
They are also unable to travel freely. The military demands that they obtain an official permit even to travel to the next town.
It is almost impossible for them to get permission to travel outside northern Rakhine.
Rohingya are subjected to routine forced labour.
The amount of time they have to give varies, but Chris Lewa at the Arakan Project says that typically a Rohingya man will have to give up one day a week to work on military or government projects, and one night for sentry duty.
This reduces the time they have to earn a living for their families. Burmese Buddhists living in the area are usually not required to do this.
The Rohingya have also lost a lot of arable land, which has been confiscated by the military to give to Buddhist settlers from elsewhere in Burma.
Some Rohingyas said they were beaten by the Thai authorities
One of the most bizarre forms of discrimination imposed on the Rohingya is that they must get official permission to get married.
Like all the other documents they must obtain, these give opportunities for officials to extort money from them, and the marriage approval can take two years or more.
Couples caught getting married or sleeping together without this approval can be arrested.
The Arakan Project has documented a number of cases where the men have been jailed, in one case for seven years. When they get married they are required to sign a commitment not to have more than two children.
This litany of abuse and harassment makes the Rohingya a downtrodden underclass even in Burma, one of the world's most repressive and impoverished states.
This is why 200,000 fled to Bangladesh in 1978, and another 250,000 between 1991 and 1992. There has been a steady stream into Bangladesh since then.
The Thai military's hardline approach in recent weeks has backfired badly
But the numbers heading out into the Andaman Sea by boat have increased sharply over the past two to three years.
There has been no discernable deterioration in the way the Rohingya are being treated by the Burmese authorities, as in 1978 and 1991, so other factors are driving them to leave.
Conditions for the Rohingya in Bangladesh are grim. Around 28,000 live in the two officially recognised camps, which get some assistance from the UN.
But 200,000 more eke out an existence outside the camps, in a desperately poor part of Bangladesh, with no official documentation, and no prospect of employment.
In the past they have made their way to the Middle East, especially Saudi Arabia, in search of work, as many Bangladeshis do.
They could do that because it was relatively easy to obtain Bangladeshi passports. But heightened security concerns in Bangladesh and Saudi Arabia over Islamic extremism have made it far more difficult for the stateless Rohingya to travel.
Instead they have been making their way to Malaysia by boat.
There are already around 20,000 Rohingya in Malaysia, and the UN has had some success in protecting them from deportation.
The job prospects there are better than Bangladesh, and this slim hope of a better life is what is now driving thousands to take the risky journey across the Andaman Sea.
Many who make the perilous journey at sea come close to death
Inevitably some have landed in Thailand instead. Others have been intercepted by the Thai navy once they entered its territorial waters, which lie en route to Malaysia.
Networks of brokers have grown to cash in on this hope; they charge up to $800 (Ł547) to make the trip in rickety and overcrowded boats.
Shortages of food and higher prices over the past year in northern Rakhine state are also driving more people to flee.
Of the Rohingya survivors being washed up in Indonesia and the Andaman Islands after being set adrift by the Thai security forces, some left Bangladesh, some left Burma, and a few had been rounded up in Thailand after living there for some time.
The scandal over Thailand's treatment of the Rohingya has at least brought their plight some rare publicity.
It has also brought home to Thailand and Burma's other neighbours that the unending repression inside Burma affects them far more than anyone else, and that the Rohingya are a regional problem which requires a concerted regional response.
Whatever horrors they may have endured recently in the Andaman Sea, the flow of Rohingya boat people is unlikely to stop.