A prominent Thai mayor has been arrested over a human trafficking scandal exposed by the discovery of mass graves in southern Thailand.
Banjong Pongphon was a "key suspect" in the investigation who "wielded great influence" in the area, police said.
The UN refugee agency said on Friday that 25,000 migrants boarded people smugglers' boats from Myanmar and Bangladesh in 2015's first quarter.
This was about double the number who left over the same period in 2014.
Banjong Pongphon is mayor of Padang Besar, a sub-district in southern Songkhla province where 26 bodies were exhumed from mass graves last week.
Smugglers' camps in the forests and plantations surrounding Padang Besar are among the main destinations of the migrants, according to a report by the UN High Commissioner for Refugees (UNHCR).
It is not yet clear what those exhumed from the graves discovered in Songkhla died from. The UNHCR report said that over half of the migrants interviewed by the UN who had travelled since October last year knew at least one person who had died in the smugglers' camps, mainly as a result of illness, beatings or being shot for trying to escape.
'Heads will roll'
Police chief General Somyot Poompan told a meeting at Thailand's police headquarters in Bangkok on Friday that police will be dealt with severely if they are found to be colluding or ignoring people smuggling.
"If you are still neglecting, or involved with, or supporting or benefiting from human trafficking networks - your heads will roll," he said.
Referring to the transfer on Thursday of dozens of police pending an investigation, Gen Somyot said: "To remove about 50 officers from their posts isn't something I want to do, but it's something I have already warned you about.
"I have warned you but you didn't listen. I have warned but you still did it," he said.
In addition to the 50 officers removed, eight people, including Mayor Banjong, have been arrested.
Those found in the graves are thought to be migrants from Myanmar and Bangladesh. Those from Myanmar, formerly known as Burma, are thought to be minority Rohingya Muslims fleeing persecution in their own country.
The Thai military junta has given local authorities until the end of next week to eradicate camps used by smugglers.