The CIA has released documents which for the first time formally acknowledge its role in a 1953 coup which ousted prime minister Mohammad Mossadeq of Iran.
The documents were published on the National Security Archive on the 60th anniversary of the coup. They came from the CIA's internal history of Iran from the mid-1970s.
The US role in the coup was openly referred to by then-Secretary of State Madeleine Albright in 2000, and by President Barack Obama in a speech in Cairo in 2009.
But NSA editor Malcolm Byrne said until now, intelligence agencies had issued "blanket denials" of their role.
The BBC reports the documents were obtained by the NSA under the Freedom of Information Act. This is believed to be the first time the CIA has itself admitted the part it played in concert with MI6.
Mr Mossadeq was elected in 1951 and he renationalised Iran's oil production, which had been under British control through the Anglo-Persian Oil Company - which later became British Petroleum (BP).
The BBC reports that was a source of serious concern to the United States and Britain, which saw Iranian oil as key to its post-war economic rebuilding. The Cold War was also a factor in the calculations.
The coup strengthened the rule of Shah Mohammad Reza Pahlavi - who had fled Iran following a power struggle with Mr Mossadeq. He returned after the coup and became a close ally of the United States.
US and UK intelligence agencies bolstered pro-Shah forces and helped organise anti-Mossadeq protests.