More than 250 people from 20 nationalities who had been working in telecom fraud centres in Myanmar's Karen State have been released by an ethnic armed group and brought to Thailand.

The workers, more than half of whom were from African or Asian nations, were received by the Thai army, and are being assessed to find out if they were victims of human trafficking.

Last week Thai Prime Minister Paetongtarn Shinawatra met Chinese leader Xi Jinping and promised to shut down the scam centres which have proliferated along the Thai-Myanmar border.

Her government has stopped access to power and fuel from the Thai side of the border, and toughened up banking and visa rules to try to prevent scam operators from using Thailand as a transit country for moving workers and cash.

Some opposition MPs in Thailand have been pushing for this kind of action for the past two years.

Foreign workers are typically lured to these scam centres by offers of good salaries, or in some cases tricked into thinking they will be doing different work in Thailand, not Myanmar.

The scammers look for workers with skills in the languages of those who are targeted for cyber-fraud, usually English and Chinese.

They are pressed into conducting online criminal activity, ranging from love scams known as "pig butchering" and crypto fraud, to money laundering and illegal gambling.

Some are willing to do the work, but others are forced to stay, with release only possible if their families pay large ransoms. Some of those who have escaped have described being tortured.

The released foreign workers were handed over by the Democratic Karen Benevolent Army, DKBA, one of several armed factions which control territory inside Karen State.

These armed groups have been accused of allowing the scam compounds to operate under their protection, and of tolerating the widespread abuse of trafficking victims who are forced to work in the compounds.

The Myanmar government has been unable to extend its control over much of Karen State since independence in 1948.

On Tuesday, Thailand's Department of Special Investigation, which is similar to the US FBI, requested arrest warrants for three commanders of another armed group known as the Karen National Army.

The warrants included Saw Chit Thu, the Karen warlord who struck a deal in 2017 with a Chinese company to build Shwe Kokko, a new city believed to be largely funded by scams.

The BBC visited Shwe Kokko at the invitation of Yatai, the company which built the city.

Yatai says there are no more scams in Shwe Kokko. It has put up huge billboards all over town proclaiming, in Chinese, Burmese and English, that forced labour is not allowed, and that "online businesses" should leave.

But we were told by local people that the scam business was still running, and interviewed a worker who had been employed in one.

Like the DKBA, Saw Chit Thu broke away from the main Karen insurgent group, the KNU, in 1994, and allied himself to the Myanmar military.

Under pressure from Thailand and China, both Saw Chit Thu and the DKBA have said they are expelling the scam businesses from their territories.

The DKBA commander contacted a Thai member of parliament on Tuesday to arrange the handover of the 260 workers.

They included 221 men and 39 women, from Ethiopia, Kenya, the Philippines, Malaysia, Pakistan, China, Indonesia, Taiwan, Nepal, Uganda, Laos, Burundi, Brazil, Bangladesh, Nigeria, Tanzania, Sir Lanka, India, Ghana and Cambodia.