US President Barack Obama reiterated Thursday that $400 million that the United States helped airlift to Iran early this year was not a ransom for the release of American prisoners.

"Some of you may recall we announced these payments in January. Many months ago. They were not a secret," he told a press conference at the Pentagon, adding that the United States does not pay ransom.

The White House has previously said the payment was returning cash from a 1970s Iranian military order that was not fulfilled because of the Islamic Revolution.