Thai authorities said Tuesday that they were testing the DNA of a Japanese man at the centre of a "baby factory" scandal to determine if he is the biological father of the nine infants.
Thai police are seeking to question the man -- who has since left the country but voluntarily sent the DNA sample -- about the mysterious discovery earlier this month of the nine babies in a Bangkok apartment.
Five other babies previously cared for at the same property are thought to have already been taken out of the country.
Police Major General Naiyawat Phadermchit said officials were awaiting the result of the DNA test.
"The police investigators sent it to the forensic experts of the national police to check and compare," he told reporters.
"We will inform you when we have any more information," he added.
According to the Japanese weekly magazine Shukan Post, the man is the son of a Japanese IT millionaire.
His lawyer Kong Suriyamontol submitted the DNA sample on his behalf to Thai police on Monday.
The sample was collected in Japan "by a respected relevant organisation", Kong added.
Kong said he had also submitted a written explanation from the Japanese man to the police, without divulging the content.
Police Colonel Witawat Chinkham told AFP that the Japanese man claimed to be the father of all the babies.
The case is the latest twist in a widening surrogacy scandal initially triggered by accusations that an Australian couple abandoned a baby born with Down's syndrome with his Thai surrogate mother -- but took his healthy twin sister.
David Farnell, 56, and his wife have denied deliberately leaving the boy, called Gammy, with the surrogate mother, who was paid around $15,000 to carry the twins.
Paid surrogacy is illegal in Thailand and the kingdom's army rulers have vowed to introduce a new law that could result in 10 years' imprisonment for anyone found guilty of involvement in the trade.
Australia has asked Thailand to make "transitional arrangements" to help any of its citizens who have already entered into surrogacy arrangements.
Last week a gay Australian couple were stopped from leaving Thailand with a baby because they had incomplete documents.