Thai officials estimate there are 250 current cases involving Thai surrogate mothers and their foreign biological parents, 150 of them Australians.

The talks under way in Bangkok come as Thai authorities revealed the Thai doctor responsible for the birth of Gammy and his twin sister has carried out hundreds of the procedures.

"I don't know the exact number this doctor has performed but it's in the hundreds," said Boonreung Trireungworawat, permanent secretary of Thailand's Health Department.

The doctor has not been named.

Mr Boonreung said most of the cases involving illegal surrogates in Thailand have being handled by one clinic in central Bangkok that was raided by Thai authorities earlier this week.

"While surrogacy is not illegal in Thailand, it is illegal for these clinics to offer these procedures without authorisation from the ministry," he said.

As part of a sweeping crackdown on surrogacy in Thailand, clinics found to have performed operations without the proper permits would have their medical licences cancelled, he said.

Thailand's strict military rulers are moving quickly to close down the country's booming surrogacy business.

They have made the passing of a draft law banning commercial surrogacy and IVF gender selection a priority for the first sitting of Thailand's military-dominated interim parliament later this month.

Prominent child rights and protection activist Paveena Hongsakul, a former government minister, has called for an urgent investigation into what she called "surrogacy for hire" that could be used for the potentially fatal extraction of foetal fluid to provide stem cells.

She also called for an investigation into the case of a woman who was paid for a surrogate pregnancy but lost the baby seven months into the pregnancy, to establish whether the foetus' spinal fluid was extracted for the manufacture of cosmetics.