"Given the track record, if they continue on the trend and pathway that they've been on, I don't think anybody's going to hold their breath," McCormack told reporters when asked about proposals it presented to the European Union.
"But one, again, would hope that they decide to change course in the face of mounting costs to Iran for its behavior that is clearly outside the lines of acceptable behavior in the international system, as defined by three Security Council resolutions," McCormack said.
Iran must in any case yield to UN Security Council resolutions, which demand it halt the enrichment of uranium, McCormack added. Washington claims the program is to build an atomic bomb, while Tehran insists it is for electricity.
"And in terms of the Iranian proposal, they know what the requirements are. It's been clearly stated in the Security Council and IAEA (International Atomic Energy Agency Board of Governors' statements and resolutions," he said.
"They know what the bar is. Thus far they have not even come close to getting over the bar. But we shall see," McCormack said.
In Brussels, Iran's ambassador to the European Union, Aliasghar Khaji, presented a new package of proposals aimed at solving the world's "collective challenges", including nuclear energy, a statement said.
He gave the package "on the management of global challenges" to EU foreign policy chief Javier Solana during talks on Tuesday, the Iranian embassy statement said.
The proposals contained "the points of view of our country toward the great global difficulties on several political, security, economic and energy levels, and on the question of the peaceful use of nuclear energy," it said.
Since June 2006, Solana has been tasked by the five UN Security Council permanent members — United States, Russia, China, Germany, Britain, France — as well as Germany to negotiate with Iran over its disputed nuclear program.
