Vietnamese police are investigating the case of a 13-year-old girl who is allegedly being detained for ransom to cover her father's gambling debts in Cambodia, Phap Luat newspaper reported.

According to police, Nguyen Thi Thuy Kieu of Ho Chi Minh City's Cu Chi District was allegedly kidnapped and taken to a Cambodian casino on November 18.

Tran Thi Dao, Kieu's grandmother, reported to police that her son, Nguyen Van Lam, was a serious gambling addict. After Lam and his wife separated, Kieu went to live with her grandmother.

On November 18, Kieu did not return home after school as usual. Dao and Dinh Thi Hoa, Kieu's mother, searched for her everywhere to no avail.

That night, Dao received a phone call from an unidentified number, a man claiming that Kieu and Lam were being held captive in the Bay Tang Casino where Lam lost VND100 million (US$4,750) gambling.

Dao then put Kieu on the phone; the young girl calling for help.

The man told Dao she must pay the debt immediately; otherwise interest would be added each day. He threatened to sell Kieu to a brothel in Thailand if the debt is not paid quickly.

Hoa also received a phone call saying her husband voluntarily delivered his daughter to the casino, as collateral or payment of his gambling debts.

According to Dao, three days before Kieu went missing, two men came to Lam's house and he left home with them.

On the morning of November 18, Kieu was at school when Lam came and picked her up, according to a teacher. The two have not been seen since, Dao said.