Iran announced Tuesday plans to restart sensitive nuclear research activities, a move that threatens an agreement with European negotiators and tests the will of the international community to punish the country. The decision, contained in a letter delivered Tuesday to the International Atomic Energy Agency, the United Nations' nuclear monitoring agency, in Vienna, declared that Iran "has decided to resume" research and development "on the peaceful nuclear energy program" that was suspended under an agreement with France, Germany and Britain in late 2004.

The letter did not define the research and development, but said that the activities would resume next Monday and be conducted "in accordance with Iran's safeguards agreement" with the agency. To that end, it requested that the agency "take necessary and timely preparation." Iran has argued all along that its decision to enter into an agreement with the Europeans to suspend all uranium conversion and enrichment activities was temporary, not required under its international treaty obligations and dependent on receiving a broad range of economic, technological, political and security incentives that it claims have not been forthcoming.

Indeed, in defending Iran's action, the letter said that the suspension of the country's nuclear-related activities under the European agreement had been "voluntary and non-legally binding." But the United States, and to an increasing extent the Europeans, are convinced that Iran is determined to become a nuclear power, and they have taken a more forceful stance in trying to ban Iran from conducting all nuclear activities that could help in a weapons program.

Iran's most recent decision is certain to further erode foreign confidence in the country's leadership. Iran's President, Mahmoud Ahmadinejad, has opened himself up to fierce international condemnation with his inflammatory statements that the Holocaust is a myth and that Israel should be wiped off the map. Last Sunday, Ahmadinejad said that Europe had decided to create a "Jewish camp" in the midst of Muslim countries as the best way to rid Europe of Jews.

Last August, Iran angered its European negotiating partners and the United States when it resumed the process of converting uranium at its site at Isfahan, a clear violation of the European agreement, but only a preliminary step in mastering the nuclear fuel cycle.

The latest Iranian move will complicate a Russian initiative to break the deadlock between Iran and the Europeans over whether Iran has the right to enrich uranium. Russia has proposed that Iran be allowed to conduct uranium enrichment activities in Russia and promised to guarantee that Iran's nuclear program is peaceful. A nuclear delegation from Moscow was scheduled to arrive in Tehran for talks this weekend.

Criticism of Iran's decision to restart nuclear research and development activities was swift. A statement from the British Foreign Office called the announcement "unhelpful and provocative." Cristina Gallach, a spokesman for the EU, called the decision "a step in the wrong direction."

France called on Iran to reverse the decision. "We would like Iran to abide by the suspension of all activities related to enrichment and reprocessing," said a Foreign Ministry spokesman, Jean-Baptiste Mattei.

Mohamed ElBaradei, director of the International Atomic Energy Agency, called on Iran to maintain "its suspension of all enrichment- related activity as a key confidence-building measure," and to resolve other outstanding issues about its nuclear program.

The agency has repeatedly criticized Iran for failing to fully cooperate with requests to open up certain facilities to its inspectors. It has summoned Iranian officials to a meeting in Vienna on Wednesday so that they can explain their intentions on research activities, according to two agency officials, who spoke on condition of anonymity because of the sensitive diplomacy involved.

"Research" has been a code word for modest experiments in enrichment at the previously secret facility at Natanz in central Iran. Agency officials expressed particular concern that Iran intends to reopen that site, perhaps to conduct modest enrichment experiments or to manufacture and assemble centrifuges for uranium enrichment, the most sensitive part of the nuclear fuel cycle.

In a proposal presented last spring to the three European governments, Iran outlined steps that it said would both advance its nuclear program and provide assurances that its program was peaceful. Among the proposals was the installation of 3,000 centrifuges at Natanz.

On Monday, the head of the Parliament's national security commission, Alaeddin Borujerdi, said Iran was "determined" to reactivate the Natanz facility.

Iran could be gambling that even if it restarts nuclear research activities, it can once again escape international sanction. The United States and the Europeans threatened to take Iran to the UN Security Council for punitive action after it resumed activities at Isfahan but were forced to back down in the face of opposition from China and Russia, which have veto power on the council.

In Tehran on Tuesday, Mohammad Saeedi, deputy head of Iran's atomic energy agency, said on state television that Iran would resume "research," without providing further detail. But he stressed that the research "has no connection with production of nuclear fuel," adding, "That is a separate issue on which no decision has yet been made." He also portrayed the decision as one of national self-interest, saying that the suspension of key nuclear activities under the agreement with the Europeans had hurt Iran. "During this period our experts incurred heavy losses and many of our researchers have lost their jobs," he said.

The letter to the International Atomic Energy Agency was written on stationery of the Permanent Mission of Iran to the United Nations in Vienna.

Parts of the letter were quoted in an agency news release; parts were disclosed by a European diplomat who spoke on condition of anonymity because of the sensitivity of the nuclear issue. Agency officials described the letter's contents to representatives of the 35 countries that make up its board, which could censure Iran by referring its case to the Security Council.