"That's not something from the United States that's on the table," State Department spokesman Sean McCormack told reporters when asked about European willingness to present Iran with incentives tied to security.
On Monday, EU foreign policy chief Javier Solana said in Brussels that the European Union was preparing a "bold package, that will contain issues relating to nuclear, economic matters, and maybe, if necessary, security matters".
But McCormack said the US was not considering offering assurances over security.
"I'll let others speak for themselves," McCormack said. "But from the United States, that's not on the table."
He recalled President George W. Bush's oft-repeated position that no option is off the table, including the military option.
Earlier Wednesday Iran's hardline President Mahmoud Ahmadinejad ridiculed the EU plan during a rally in Arak, Iran, saying, "They say they want to give us incentives. They think they can take away our gold and give us some nuts and chocolate in exchange."
When asked about the comment, McCormack said: "I think that once this is presented to the Iranian regime, we will have at least a better idea of what their intent is."
McCormack also said that the five permanent members of the UN Security Council plus Germany would meet on Tuesday to work out a common approach on Iran.
The discussions on Iran were initially scheduled for Friday but the State Department spokesman said the six countries needed time to prepare contingency plans depending on how Iran responds to the package of incentives and penalties.
He said diplomats from the major powers were trying to "talk through" the question of "how would the international community react to either Iran agreeing to this package of incentives or rejecting this package of incentives?"