One of the greatest security challenges facing the transatlantic community today is posed by the leaders of Iran and their atomic ambitions.

Iran's determined pursuit of nuclear weapons capabilities threatens the world's non-proliferation regime and the stability of a region already vexed with violence and volatility.

Imagine a leadership, that spreads death through terrorism, that threatens death to whole countries, armed with the most deadly of weapons. Six months ago, the International Atomic Energy Agency made two important findings:

-- First, that Iran has violated its international obligations; and

-- Second, that Iran has lost international trust in the peaceful nature of its nuclear program.

Last month, after giving Iran multiple opportunities to address international concerns, the Agency's Board reported these findings to the UN Security Council. The Board also reported a list of steps required of Iran to begin regaining international confidence. These steps included:

-- Suspending uranium enrichment, including research and development, for which Iran today has no civil requirement;

-- Reconsidering construction of a new research reactor, which Iran does not need for peaceful use, but can produce weapons-grade plutonium;

-- Ratifying promptly and implementing in full the Additional Protocol, to help the Agency resolve outstanding questions;

-- Implementing transparency measures requested by Dr. ElBaradei, including access to individuals, documents, dual-use equipment, and military facilities.

Iran's leaders had a month to meet these requirements. At the Board's meeting this month, Dr. ElBaradei reported that Iran's leaders failed to meet a single one. The Director General's report demonstrates why Iran's nuclear program is on the Security Council's agenda.

-- First, after three years of intensive IAEA efforts, the Director General is unable to certify the peaceful nature of Iran's program. Troubling issues remain unresolved; including Iran's connections to the A.Q. Khan network a black market for nuclear weapons technologies. New issues have been uncovered, including ones with a military dimension.

-- Second, Iran's cooperation remains forced and incomplete. Iran has refused to document its activities and give access to key individuals. It has refused to turn over documentation on manufacturing nuclear weapons components. Its stories are incomplete and inconsistent with other information available to IAEA inspectors.

-- Third, and perhaps most troubling, Iran's leaders are forging ahead to acquire the material, equipment, and expertise to produce nuclear weapons.

The Director General reported that Iran has now stockpiled 85 metric tons of uranium hexafluoride and continues to produce more. According to estimates by the International Institute of Strategic Studies, 85 metric tons is enough, if enriched, to produce ten nuclear weapons. The Director General also reported that Iran has begun enrichment and plans to start installing 3,000 centrifuges by the end of this year.

According to IISS estimates, a 3,000-centrifuge cascade can produce enough material for a nuclear weapon in less than a year. Even a smaller cascade can serve as the first installment toward a large-scale breakout capability or as a testing ground for undeclared cascades assembled in covert locations.

The Director General's report has been transmitted to New York for action by the Security Council. There we are working with the countries of Europe and from elsewhere around the world to bring the Security Council's weight to bear. The aim is to reinforce the authority of the IAEA and to demonstrate to Iran's leaders, that by failing to heed international concern, they are isolating their country and risking international sanction.

The opportunity for a negotiated solution is still on the table. It was first offered by the European Union, augmented by Russia, and supported in each case by the United States. We need to convince the leadership in Tehran to grasp this opportunity and benefit from international offers of nuclear energy assistance, nuclear fuel assurances, and new political and economic engagement.

Instead, the leaders in Tehran have thus far chosen a course of phony negotiation and flagrant threats. They hoped to divide the international community and leave unchecked their ambitions for nuclear weapons. They hoped to negotiate diplomatic cover to master the technology for centrifuge enrichment. Instead, their defiance has increasingly united the international community, leaving Iran increasingly isolated and subject to Security Council action. The people of Iran deserve better.

Our goal remains a diplomatic solution, one that benefits not only the Iranian people, but also regional stability and the nonproliferation regime. But the leadership in Tehran is determined and defiant, and not readily moved by diplomatic demarche. For diplomacy to succeed, transatlantic unity will be crucial, together with a common resolve to use the full range of diplomatic tools available to the Security Council.