UNITED NATIONS — A defiant Iran said yesterday that it is determined to hold on to all of its nuclear program, including uranium enrichment, and lashed out at the United States for trying to limit its efforts.

At a United Nations conference on the future of the nuclear Non-Proliferation Treaty, Iranian Foreign Minister Kamal Kharrazi also accused the United States and Israel of posing the greatest threat to international security with their arsenals of nuclear weapons.

Israel, which neither admits nor denies having the bomb, is estimated to have 200 warheads. The United States has about 10,000.

Kharrazi's comments heightened tensions over the nuclear issue as officials in Iran indicated they were ready to end a suspension of some of their nuclear programs.

"We will definitely restart some activities," Foreign Ministry spokesman Hamid Reza Asefi said. He didn't specify which operations would resume or when but added that uranium enrichment "will remain the last option."

European officials reacted cautiously, suggesting the comments had more to do with Iranian domestic politics than with a desire to break off negotiations with Europe.

But one senior European official said that if Iran begins uranium enrichment — processing uranium gas through centrifuges to produce either fuel for nuclear power or the stuff of atom bombs — it is likely that Britain, France and Germany will consider negotiations they have pursued for years with Iran terminated.

Rising tensions about Iran and North Korea, which has said it has nuclear weapons, dominated the opening of a monthlong U.N.-sponsored conference on the Non-Proliferation Treaty, the cornerstone of atomic-disarmament pacts.

Under the 35-year-old treaty, states without nuclear weapons pledge not to pursue them in exchange for a commitment by five nuclear powers — the United States, Russia, Britain, France and China — to move toward nuclear disarmament. Three other nuclear states — Israel, India and Pakistan — remain outside the treaty.

The treaty is reviewed every five years at conferences whose consensus positions give valuable political support to nonproliferation initiatives.

The United States on Monday pressed the 188 attending nations to ensure Iran and North Korea are denied peaceful nuclear-energy benefits because they had violated the treaty.

The Bush administration and its European allies share the goal of keeping Iran from acquiring the ability to produce nuclear weapons but have taken different approaches to head off that possibility. After revelations three years ago that Iran had secretly operated a nuclear program for nearly 20 years, the United States decided against engaging Iran in talks, instead taking a hard line.

However, its efforts to isolate Iran and haul it before the United Nations Security Council for possible punitive action failed because of a lack of international support. President Bush switched tactics in February, agreeing to support the European negotiating effort but not join it directly.

The countries have been trying to get Iran to permanently abandon enrichment in exchange for economic and political incentives.

U.S. officials who spoke on the condition of anonymity said that French Foreign Minister Michel Barnier assured Secretary of State Condoleezza Rice during a meeting yesterday in Washington that if Iran makes good on its promises, France would support taking the matter to the Security Council to discuss possible sanctions, a move the Bush administration has been pushing for and the Iranians had hoped to avoid.

Barnier also said France thought a showdown could be avoided. But one U.S. official said the administration began working yesterday on options for Security Council action, which could include warnings to Iran or the threat of economic sanctions if the nuclear program continues.

Under the terms of the nuclear treaty, countries that forgo nuclear weapons are eligible for sensitive nuclear technology as long as it is used for peaceful energy programs. Iran maintains that it is adhering to that arrangement, but the Bush administration said Monday that Iran should not be allowed to benefit from it any longer because it spent 18 years building nuclear facilities in secret.

Iran's main nuclear site was exposed by a dissident group in 2002, fueling suspicions about the Islamic republic's true intentions and setting off a two-year investigation by U.N. inspectors. The inspectors said they found no proof Iran is trying to build nuclear weapons. But the Bush administration hasn't accepted those findings or Iran's claims.

"The only way to really satisfy and reassure the world that they're not going to be a nuclear threat is to eliminate those programs," State Department spokesman Richard Boucher said yesterday.

Kharrazi, who chose to deliver his speech to the nuclear conference in English, rather than his native Farsi, said that wouldn't happen.

Iran is "determined to pursue all legal areas of nuclear technology, including enrichment, exclusively for peaceful purposes," he said.

It is wrong, Kharrazi said, to limit "access to peaceful nuclear technology to an exclusive club of technologically advanced states under the pretext of nonproliferation."

The United States, pointing to Iran's huge oil reserves and initial efforts to conceal its enrichment activities, questions Iran's need to develop nuclear power.

Iranians have been seeking ways to hold on to nuclear technology. The country suggested last week it be allowed to keep 3,000 centrifuges, which would give Iran the capability to enrich large quantities of uranium. As part of such an arrangement, Iran would operate the centrifuge cascade under 24-hour surveillance by U.N. inspectors.

Compiled from The Washington Post, Los Angeles Times, The Associated Press and Reuters reports.