The US embassy in London has moved to clarify remarks made by its ambassador about the transfer of terror suspects to other countries for interrogation.
Mr Tuttle made the remarks on the BBC's Today programme
Robert Tuttle told the BBC there was no evidence of "extraordinary renditions" to Syria, which has been criticised by Washington for its human rights record.
The US embassy later said Mr Tuttle recognised there had been a media report of a rendition to Syria.
It did not condone torture, nor did US officials take part, it added.
The embassy said it did not comment on specific cases.
Canadian citizen Maher Arar was detained as a terrorist suspect in New York in 2002 and then flown to Jordan, before being transferred to Syria.
He was released a year later following the intervention of the Canadian government.
Mr Arar claims he was tortured while in Syrian custody.
BBC Washington correspondent Jonathan Beale said the ambassador's comments and the US embassy's subsequent clarification would once again raise questions about the practice of extraordinary renditions.
"An issue which has already caused strains between America and its European allies," he said.