"I do not think we have a final answer yet. We are going to be looking for a definitive response from the Iranian government via Mr. Solana. We have not received yet," State Department spokesman Sean McCormack said at a briefing.

Javier Solana, the EU's foreign policy chief, presented to Teheran the package that contains both incentives and possible penalties if Iran does not cooperate.

"We certainly continue to hope that the Iranian government would take the opportunity presented to it, the two pathways presented to it, take the pathway of negotiation, which is certainly the positive pathway," the spokesman said.

Iran sent out mixed messages on Thursday over the nuclear package. Iranian Supreme Leader Ayatollah Ali Khamenei vowed not to give up its nuclear program, but President Mahmoud Ahmadinejad, while in Shanghai, said Iran is ready to negotiate over the nuclear standoff.

The United States has urged Iran to accept the offer, or the nuclear issue will go to the United Nations Security Council for possible sanctions on Iran.