Four couples from the United States and Australia have been prevented from leaving Thailand with surrogate babies as part of a government crackdown on the burgeoning commercial surrogacy industry, an Australian broadcaster reported on Friday.

The crackdown follows recent publicity over a Thai surrogate mother who said she was left with a baby rejected by his Australian biological parents after he was born with Down syndrome. The biological parents, who took the boy's healthy twin sister home, dispute the circumstances in which they abandoned their son.

Two Australian same-sex couples were prevented by Thai officials from leaving Bangkok's international airport on Thursday afternoon with babies born to Thai women, Australian Broadcasting Corp reported. One couple had attempted to travel with the Thai surrogate mother in hopes of avoiding a challenge at the immigration desk, ABC said.

Two US couples also were prevented from leaving Thailand with babies under similar circumstances since Wednesday, ABC said.

Thai officials told ABC the couples would have to apply for court orders to take the babies from the country, a process that could take months.

Thailand Immigration police spokesman Colonel Voravat Amornvivat said the Bangkok airport's immigration departure section had no record of Australian couples with surrogate babies who were barred from leaving Thailand. He said, however, that it might be possible that it was not flagged in the system.

"If it did happen, it could be because the couples could not provide sufficient documents to prove that the babies are theirs,"Voravat said. "Under Thai law, in order to take an infant out of the country, it has to be proved that the infant is traveling with or accompanied by the parents. And due to the recent surrogacy issue, the authorities are stricter in keeping an eye on those leaving the country."

Melissa Sweeney, a spokeswoman for the US embassy in Bangkok, said in an e-mail that the embassy was aware of reports that some parents with children born to surrogates have not been permitted to leave Thailand with them. Embassy officials were seeking clarification about Thailand's immigration requirements and talking to Thai government authorities to determine what the ramifications may be for US parents who have already entered into surrogacy agreements in Thailand, she said.

Australia's Department of Foreign Affairs and Trade on Friday would not confirm the ABC report, citing privacy reasons.

"We strongly urge Australians entering Thailand for the purposes of commercial surrogacy to seek independent legal advice in both Thailand and Australia before doing so,"the department said in a statement. "In particular, they should seek advice on the implications of any new exit requirements."

Scores of Australian biological parents are currently pregnant through surrogates in Thailand.