A Thai surrogate mother left with a Down's syndrome baby who was abandoned by his Australian biological parents has expressed concern for the infant's healthy twin due to reports the father is a convicted sex offender.

Pattaramon Chanbua has been bringing up baby Gammy as her own since he was born in December.

The 21-year-old said the twins' father rejected Gammy while taking his healthy sister home to Western Australia state.

Australia's Nine Network television has reported that the father is a convicted paedophile while a police officer told the Associated Press that the father is a convicted sex offender.

The case has caused intense public interest in Thailand and Australia, and Ms Pattaramon made her views known at a news conference in her home town.

While she had previously said she was happy to have the twin girl stay with the Australian parents, the reports about the father's past have raised doubts in her mind.

"Personally, when I heard the news I was shocked but I can't say anything much right now," she said, adding that she would "leave it to the law" to see if she can get the girl back.

The process appeared to have been carried out legally under contract in Thailand and Western Australia, though other states in Australia do not allow it.

Ms Pattaramon also expressed sentimental attachment to the child, saying: "I want her back because she is my baby. She was in my womb."

However, she said she was inclined to leave the resolution of the issue up to "fate" and what was best for the baby girl.

"If she is happy, then I, as a mother, am also happy. I don't want to bring her back to suffer or anything. A mother would never want her child in trouble," she said.

"But if she really cannot go on living there, then I'm very happy to have her back in my arms."

She said she will never hand over to the Australian couple seven-month-old Gammy, who was born with a congenital heart condition as well as Down's syndrome: "Never. Not in any way."

The case had already caused a stir because of the idea that the Australian couple had abdicated their responsibility by not taking home both children.

They have not come out publicly to speak about the case, though Australian broadcaster ABC reported that Gammy's biological father has denied intentionally abandoning his son in Thailand, saying he did not know that his daughter had a twin.

Ms Pattaramon has said she did not receive the full payment she was promised for serving as a surrogate mother.

An online campaign by the Australian charity organisation Hands Across The Water to help Gammy has raised more than 215,000 US dollars (£127,500) since July 22.