BBC correspondent, Dublin
Ireland has demanded a full explanation from Washington after a US marine was found handcuffed on board a plane at Shannon airport in the west of Ireland.
The US should have asked Dublin before transferring prisoners
The Irish government says it should have been asked for formal permission for any transfer of prisoners.
The US marine, who was also manacled, was discovered by a cleaner who boarded the plane when it stopped to refuel.
Foreign Affairs Minister Dermot Ahern said he views the incident with "the gravest concern".
Shannon airport in County Clare is regularly used for stopovers by the US military and the flight was taking 181 military personnel from Kuwait to an airbase in the US.
Most of the passengers had already disembarked when the prisoner was discovered.
The cleaner reported what she had found to her manager, who in turn called the US embassy in Dublin.
Following the incident, which took place on Sunday, the US ambassador to Ireland was called to a meeting with Mr Ahern, who is now waiting for a full written report.
The minister said such a transfer of a prisoner requires the consent of the Irish government but that did not happen.
In Ireland, the affair is politically sensitive as there has been heavy criticism of the use of Shannon by the US military.
Earlier this month, a report by the Council of Europe named Ireland among the countries allegedly used for "extraordinary rendition" involving the secret transfer of prisoners - something the Irish government denies.