Despite the threat of new sanctions, Iran is advancing work at its largest nuclear facility and has informed international inspectors in writing that it will not comply with a U.N. order to suspend the program, according to U.S. and European diplomats familiar with the inspectors' latest findings.

The U.N. Security Council on Dec. 23 set a 60-day deadline for the Tehran government to halt its nuclear work. Since then, though, Iran has installed nearly 400 centrifuges, in two separate lines, at its uranium-enrichment facility in the town of Natanz, according to several officials who agreed, on the condition of anonymity, to discuss details from the inspectors' report, which is due today.

The report to the Security Council will confirm, the officials said, that Iran is flouting the council's resolution and moving ahead with its efforts to enrich uranium.

U.S., British and French officials said they will respond to Iran's defiance by pressing for additional economic sanctions, including an enforced travel ban on senior Iranian officials, asset freezes, and an end to government-backed loans and credits. Secretary of State Condoleezza Rice is scheduled to meet today in Berlin with German, Russian and European colleagues to discuss the possibility of imposing those new sanctions.

"The Iranians have unfortunately not acceded to the international community's demands, and we will have to consult. We will have to decide how to move forward," she told reporters yesterday.

Rice said talks with Iran were possible on the condition that it suspend its nuclear program first.

But diplomats in Washington and at the United Nations acknowledged yesterday that they expect weeks of struggle with Russia, China and members of the European Union, all of which are ready to reopen talks with Iran even if it does not first halt the nuclear program.

"If the intention is to punish the Iranians," said one Chinese diplomat, the Security Council is in for a "long negotiating process."

A senior European diplomat said it is not a foregone conclusion that "we will go down the sanctions lane," adding: "There are quite a number of European Union countries who believe we should go easy because there seems to be an opening on the Iranian side."

The Bush administration has been trying for years to roll back Iran's nuclear advances, choosing sanctions and attempted isolation rather than engaging in direct talks with Tehran. But even with Iran clearly defying a Security Council resolution, other countries are making their own diplomatic gestures in the hopes of curtailing another Middle East crisis.

Senior diplomats from Germany, Switzerland, Russia, Saudi Arabia and China, as well as Mohamed ElBaradei, the director of the International Atomic Energy Agency, have all reached out to Iran's senior negotiator, Ali Larijani, in the past two weeks as the deadline for Iranian compliance approached.

The diplomatic impasse dampened the prospects for a swift Security Council reaction to Iran's missed deadline. Ambassador Peter Burian of Slovakia, the council's current president, said it is unlikely that the body will discuss the issue this week.

Other diplomats said that they are waiting for the results of a meeting, expected in the next 10 days, among diplomats from Russia, China, the United States, France, Britain and Germany.

Iran has said repeatedly that it wants to return to negotiations with Europe and Russia and even hold talks with the United States, but that it would not halt its nuclear program as a precondition. Larijani reiterated to ElBaradei on Tuesday that Iran is ready to commit to a three-month freeze, but only once talks resumed, officials with direct knowledge of their meeting said. Iran says that its nuclear program, which began in secret in 1987, is for the production of energy and not weapons and that the nation is within its rights, as a signatory of the Non-Proliferation Treaty, to develop nuclear fuel.

Yesterday, Iranian Foreign Minister Manouchehr Mottaki said the nuclear dispute "has to be decided peacefully with the United States." At the same time, Iranian President Mahmoud Ahmadinejad said his country will never give up its nuclear program. "Obtaining this technology is very important for our country's development and honor," he said.

Iranian officials sent a letter Monday to inspectors at the IAEA, announcing that they would not comply with the Security Council deadline and that their work at Natanz would continue, according to diplomats in Vienna, where the IAEA is based.

The Security Council has repeatedly pressed Iran since March to cease its uranium-enrichment activities. In December, the 15 nations voted to restrict Iran's trade in sensitive nuclear materials and to freeze the assets of 22 Iranian officials and institutions linked to the country's most controversial nuclear activities.

ElBaradei said in interviews published yesterday that Iran could be five to six years away from acquiring the capability to make a nuclear weapon. U.S. intelligence officials have estimated that Iran is five to 10 years away.

Lynch reported from the United Nations.