UNITED NATIONS — Iran yesterday formally rejected an American-backed package of incentives that was conditional upon its agreement to suspend all uranium enrichment activities. American officials have said such a refusal will lead to sanctions and other punitive measures.

In Tehran, the Iranian nuclear negotiator, Ali Larijani, delivered a document containing the rejection to representatives of the six countries leading the diplomacy on the crisis. Several diplomats and journalists who saw the 23-page document reported that Iranian officials wrote they would not freeze enrichment activities, which they believe are their “inherent right.”

Iranian official news agencies reporting on Iran’s response said the mullahs were ready for “serious negotiations.” The Tehran-based Fars News Agency reported that Iran rejected calls to suspend uranium enrichment, offering instead “a new formula to resolve the issues through dialogue.”

The rebuff of the incentive package, offered by the leading powers on the U.N. Security Council, came a day after the International Atomic Energy Agency announced that Iran had turned down a request by inspectors to view its underground nuclear facilities in Natanz. The refusal could constitute a violation of Iran’s obligations under the Nuclear Nonproliferation Treaty, several diplomats said.

“Although there is no justification for the other parties’ illegal move to refer Iran’s case to the Security Council,” the Islamic Republic News Agency said, “we prepared the answer to the proposed package positively on the recommendation of [the U.N. Chief] Mr. Kofi Annan.”

Secretary-General Annan had called Iran’s top officials and urged them to “respond positively” to the West’s offer of economic benefits and diplomatic openings, his spokesman, Stephane Dujarric, said. Mr. Dujarric neither confirmed nor denied yesterday that Mr. Annan is planning to visit Tehran soon as part of his efforts to reach a lasting agreement to bring an end to the Israel-Hezbollah war.

White House officials said yesterday that they would not respond officially until they had carefully studied the Iranian document. “This should be the definitive response, and we’ll move on the basis of our reading of it,” the American U.N.ambassador, John Bolton, said.

America and the other leading members of the council “made it clear” to Iran that “their unwillingness to give up their pursuit of nuclear weapons will result in our efforts in the Security Council to obtain economic sanctions against them,” Mr. Bolton said. If Iran rejects the package, he added, the council is ready to “proceed, as the ministers have agreed, with economic sanctions.”

At a meeting in Paris last month, the foreign ministers of five countries — Britain, France, China, Russia, and Germany — joined America in demanding that Iran announce a freeze on enrichment activities by August 31 or suffer sanctions and other punitive measures.

The ambassadors of those five countries in Tehran — as well as Switzerland, which represents America’s interests in Iran — received Iran’s answer yesterday, a week prior to the expiration of the deadline.

Since the Paris meeting, however, Chinese and Russian diplomats, who have in recent years urged a cautious approach toward Tehran, have begun to backtrack, saying punitive measures were not included in the final Paris declaration.

Nevertheless, Undersecretary of State Nicholas Burns made clear on Monday that an Iranian rejection of the package would lead to a council resolution imposing sanctions in September.

An American diplomat speaking on condition of anonymity told The New York Sun yesterday that he did not expect serious opposition from Moscow to some form of punitive action against Iran. “The Russians will sign on to some sanctions,” the diplomat said. “The big question is, what kind of sanctions?”

One official who saw the document but said he was unauthorized to speak about it, characterized the Farsi-language response as “very long and full of inherent contradictions.” In the document, he said, “the Iranians argue that they would love to cooperate,” but then they add that they will not give up what they call “our elementary right” to experiment with uranium enrichment.

“Iran’s most recent refusal to halt production of enriched uranium is a transparent effort to buy yet more time to cross the nuclear threshold,” said Ileana Ros-Lehtinen, a Republican of Florida who heads the House Subcommittee on the Middle East and Central Asia.

“It clearly shows that attempts to negotiate with a rogue regime such as Iran’s is fruitless; that Iran cannot be trusted; and that allowing Iran to continue such manipulation with impunity undermines global peace and security,” she added in a statement.

Israel Radio’s Farsi broadcaster Menashe Amir told the Sun that the weak response so far by the Security Council to Iran’s proxy militia, Hezbollah, emboldened the mullahs, and reduced their concerns about reaction by the so-called “international community” to their nuclear violations.