Updated

Iran's response to an incentives package aimed at defusing a dispute over its nuclear program is unacceptable, making the prospect of new sanctions more likely, U.S. officials said Tuesday.

The officials told The Associated Press that a one-page document that Iran presented to European Union foreign policy chief Javier Solana is not a definitive reply to the offer from major world powers but rather a restatement of Tehran's earlier insistence on the right to conduct peaceful nuclear activities.

The officials spoke on condition of anonymity because Solana's office has not yet characterized the document. They said the lack of a clear response means that discussion of new sanctions against Iran could begin as early as Wednesday, when senior diplomats from the six countries that made the offer will speak in a conference call to discuss the way ahead.

The United States and others accuse Iran of trying to develop nuclear weapons under cover of a civilian atomic energy program. Iran denies the charge.

The State Department said it had received a copy of the Iranian response by e-mail from Solana's office.

"We're going to take a look at it," spokesman Gonzalo Gallegos told reporters. He said the U.S. and its partners would move to impose new sanctions unless Iran's response was an unambiguous acceptance of the offer.

"We are looking for a clear, positive response from Iran and in the absence of that we're going to have no choice but to pursue further measures against them," he said.

Gallegos declined to characterize the contents of the Iranian document.

The EU diplomat said Solana had talked on the telephone with Iran's chief nuclear negotiator, Saeed Jalili, and more talks could be expected in the coming days.

On July 19, the six nations — Britain, China, France, Germany, Russia and the United States — set an informal two-week deadline for Iran to either accept or reject the economic incentives in return for curbing its uranium enrichment.

On Sunday, Iranian President Mahmoud Ahmadinejad said diplomacy was the only way out of the standoff and insisted he was serious about negotiations. Those comments came a day after he asserted his country would not give up its "nuclear rights," signaling that it would refuse demands to stop enriching uranium or at least not to expand its enrichment work.

Also Saturday, Secretary of State Condoleezza Rice said the United States would have no choice "but to begin again to prepare sanctions resolutions for the (U.N.) Security Council" if Iran did not halt the development of its enrichment program.