TEHRAN, Iran (AP) – Iran said Tuesday it was ready for “serious negotiations” on its nuclear program, but a semiofficial news agency said the government was unwilling to abandon nuclear enrichment _ the key U.S. demand.

Top nuclear negotiator Ali Larijani delivered a written response to ambassadors of Britain, China, Russia, France, Germany and Switzerland to a package of incentives aimed at persuading Iran to roll back on its nuclear program.

Larijani refused to disclose whether the response included an offer to suspend uranium enrichment, and no details of Iran’s response were released. The state-run television quoted Larijani as telling the diplomats Iran “is prepared as of Aug. 23 to enter serious negotiations” with the countries that proposed the incentives package.

But the semiofficial Fars news agency reported that Iran rejected calls to suspend “nuclear activities” _ or uranium enrichment _ and “instead has offered a new formula to resolve the issues through dialogue.”

Iran delivered its response to the incentives offer nine days before a U.N. Security Council deadline for Iran to halt enrichment or face possible economic and political sanctions.

Iranian officials close to the meeting said Iran offered a “new formula” to resolve the dispute as part of its formal response to the incentive package. The officials spoke on condition of anonymity because of the sensitivity of the information.

“Iran has provided a comprehensive response to everything said in the Western package. In addition, Iran, in its formal response, has asked some questions to be answered,” one official said, without elaborating.

European Union foreign policy chief Javier Solana said Iran’s response needs a “detailed and careful analysis,” EU foreign policy chief Javier Solana said.

In a statement, Solana said he would remain “in open contact” with Larijani.

The European response was likely to depend on how far Tehran was ready to go in suspending uranium enrichment _ the cornerstone demand of the United States, Russia, China, Britain, France and Germany, the six powers that agreed to the package of incentives if Iran compromises and punishments if it does not.

The White House deferred comment on the Iranian government’s response.

“The Security Council’s deadline is Aug. 31. I’m not going to parse the Iranian government’s document today here on the airplane,” White House deputy press secretary Dana Perino said on Air Force One as President Bush flew to Minnesota. “That is a job best left to the diplomats.”

She said the U.S. government has received a copy of the document, but that she doesn’t believe Bush had seen it yet.

At U.N. headquarters in New York, U.S. Ambassador John Bolton said the United States is prepared to quickly submit elements of a new Security Council resolution that would impose economic sanctions on Iran if it does not accept “the very, very generous offer.”

“We will obviously study the Iranian response carefully, but we are also prepared if it does not meet the terms set by the permanent five foreign ministers to proceed here in the Security Council, as ministers have agreed, with economic sanctions,” he said.

“If, on the other hand, the Iranians have chosen the path of cooperation, as we’ve said repeatedly, then a different relationship with the United States and the rest of the world is now possible,” he said.

Iran says it wants to master the technology to generate nuclear power. But critics say it is actually interested in enrichment because it can also be used to make the fissile core of nuclear weapons.

State-run television said Iran’s response meant Tehran was committed to its promises.

“Iran’s response suggests Iran is committed to dialogue and its promises. … It is in contrast with America’s policy of unilateralism,” the television said.

The six powers _ five permanent members of the U.N. Security Council plus Germany _ offered Iran the package in June. The United States is represented by Switzerland, which looks after U.S. interests in Tehran because it has not had diplomatic relations with Iran since 1979 when Muslim fundamentalists overran the U.S. Embassy.

Mohammed Saeedi, deputy head of the Atomic Energy Organization of Iran, said in comments published Tuesday that Tehran’s response would provide “an exceptional opportunity” for a return to the negotiating table for a compromise.

“Iran’s response to the package is a comprehensive reply that can open the way for resumption of talks for a final agreement,” Saeedi said.

Even so, Iran on Monday twice showed its determination to push ahead with its nuclear program, which continues under the possible threat of economic and diplomatic sanctions imposed by the Security Council if it does not halt enrichment by Aug. 31.

It turned away International Atomic Energy Agency inspectors from an underground site meant to shelter its uranium enrichment program from attack and its top leader, Ayatollah Ali Khamenei, declared that Tehran will continue to pursue its nuclear activities.

Iran has rejected the resolution passed by the council last month as “illegal,” saying a compromise can only emerge from talks.

Likewise, Saeedi’s optimistic words Tuesday were tempered by his assessment of the proposed packaged as containing “serious ambiguities” that need to be clarified in talks.

The package does not mention the part of the Nuclear Nonproliferation Treaty that affirms signatories’ right to pursue nuclear technology for peaceful purposes, Saeedi said.

The United States and some of its Western allies accuse Iran of seeking nuclear weapons. Tehran has denied the charges, saying its program is aimed at generating electricity.

The Islamic republic has repeatedly said it will never give up its right to enrich uranium and produce nuclear fuel but has indicated it may temporarily suspend large-scale activities to ease tensions.