Police in northern Greece say a 12-year-old girl has been arrested along with three of her relatives after selling her 10-week-old baby son for euro12,500 ($16,400) to undercover officers posing as adoptive parents.

A police statement said Monday that the girl, her 44-year-old aunt and her aunt's parents, aged 65 and 71, were all arrested on illegal adoption charges. The 12-year-old was expected to be released from custody after being interviewed by a public prosecutor.

The incident took place in Xrysoupoli, a town about 700 kilometers (435 miles) northeast of Athens, after police acted on a tip and used marked banknotes for the transaction. The baby was hospitalized for observation.