A U.S. woman has been detained in Ukraine on suspicion of illegally adopting of a 12-year-old girl, the border guard service said on Monday, RIA Novosti reported.

The 40-year-old woman, whose name has not been disclosed, was detained at Boryspil airport outside Kyiv after being overheard arguing with the girl, who was protesting against being taken out of the country. During questioning, the girl told police she had been mistreated by the woman.

The woman denied pressuring the girl to leave Ukraine, and said her adopted daughter was psychologically unstable.

An investigation revealed that the adoption documents had been forged, and that the girl`s adult brother had been unaware of the adoption.

The suspect will be held in Ukraine while the investigation continues.

RIA Novosti