(Adds arrests and killings in Bangladesh, and graphic link; edits)
* Refugees head for Malaysia and Indonesia after Thai crackdown
* Thailand a staging post for migrants from Bangladesh and Myanmar
* 25,000 Bangladeshis and Myanmar Rohingyas crossed in Jan-March
By Roni Bintang and Al-Zaquan Amer Hamzah
LHOKSUKON, Indonesia/KUALA LUMPUR, May 11 (Reuters) - M alaysia has detained more than a thousand Bangladeshi and Rohingya refugees, including dozens of children, police said, a day after authorities rescued hundreds stranded off Indonesia's western tip.
There has been a huge increase in refugees from impoverished Bangladesh and Myanmar drifting on boats to Malaysia and Indonesia in recent days since Thailand, usually the first destination in the region's people smuggling network, announced a crackdown on the trafficking.
Over 100 refugees from these countries were found wandering around in southern Thailand last week, apparently having been abandoned by smugglers.
An estimated 25,000 Bangladeshis and Rohingya Muslims from Myanmar boarded rickety smugglers' boats in the first three months of this year, twice as many in the same period of 2014, the U.N. refugee agency UNHCR has said. Most land in Thailand, where they are held by the smugglers in squalid jungle camps until relatives pay a ransom.
Police on the northwest Malaysian island of Langkawi, close to the Thai border, said three boats had arrived in the middle of the night to unload refugees, who were taken into custody as they came ashore. One boat was discovered after it got stuck on a breakwater, but the other two vessels escaped. There was no immediate word on the crew.
The boats contained 555 Bangladeshis and 463 Rohingya, who were being handed over to the immigration department, local police chief Harrith Kam Abdullah said.
MAGNET FOR MIGRANTS
Malaysia, one of Southeast Asia's wealthier economies, has long been a magnet for illegal immigrants.
On Sunday, nearly 600 migrants thought to be Rohingya refugees and Bangladeshis were rescued from at least two overcrowded wooden boats stranded off Indonesia's Aceh province, believing they had landed in Malaysia, authorities said.
The boats were towed to shore by fishermen after running out of fuel. Among the refugees were nearly 100 women and dozens of children.
Thai police spokesman Lieutenant General Prawut Thawornsiri said the crackdown in people smuggling had prompted the rush of arrivals elsewhere.
"Yes, our crackdown is affecting the boats," he told Reuters in Bangkok. "They are going to Indonesia. Why else would they go to Indonesia? It is so far ... Our job is to block the boats and not let them land on our shores."
Thai Prime Minister Prayuth Chan-ocha ordered a clean-up of suspected traffickers' camps after 33 bodies, believed to be of migrants from Myanmar and Bangladesh, were found in shallow graves in the south, near the Malaysian border.
Of those rescued off Indonesia, around 50 were taken to hospital. "In general, they were suffering from starvation and many were very thin," said North Aceh police chief Achmadi.
The refugees were being held in a gymnasium in the town of Lhoksukon, about 20 km (12 miles) from where they were brought ashore.
"YOU GOT WHAT YOU PAID FOR"
"We are hearing the passengers were left close to shore and were told that this is Malaysia and you got what you paid for," said Mark Getchell, head of the International Organization for Migration in Indonesia.
"They came onshore and found out it wasn't Malaysia."
An agency official estimated that around 300 people had died at sea in the first quarter of this year as a result of starvation, dehydration and abuse by boat crews.
Mohammad Kasim, a 44-year-old Bangladeshi migrant on one of the boats, told Reuters that each passenger paid 4,400 ringgit ($1,200) for the journey. Three people died on the way and were dumped in the sea.
"I worked in Malaysia for three years in construction when I was 16. I wanted to go back because it is very difficult to find work in Bangladesh," he said, speaking in Malay.
Kasim said he had left the Bangladesh town of Bogra a month ago on a small boat with 30-40 others in the hope of finding a job in Malaysia. An agency in Bogra helped arrange the trip.
They group landed on a beach in Thailand, where they stayed for 21 days before leaving on a larger ship with hundreds of passengers.
In Bangladesh, where the authorities are trying to stamp out the crisis at its source, police say they have arrested more than 100 people traffickers in recent months.
Mohammad Ataur Rahman Khandaker, a senior police officer in Teknaf, close to the Myanmar border, said that on Friday and Sunday, four "notorious" traffickers had been killed in gun fights with police. He also said three people suspected of smuggling thousands of people had been arrested in the town. (Additional reporting by Amy Sawitta Lefevre and Aubrey Belford in Bangkok; Writing by Nick Macfie; Editing by John Chalmers and Kevin Liffey)