ElBaradei said "the United States will have to step in because security assurances very much need the Americans."
The European Union has since December been trying in talks to get Iran to abandon crucial nuclear fuel cycle activities in return for a package of trade, technology and security rewards.
The United States is now backing the Europeans by offering to help out with the incentives.
ElBaradei said that "at the proper time the United States will have to be fully engaged" because "regional security (in the Middle East) is not a European affair."