Vienna, Austria ? Iran agreed to freeze its uranium enrichment program fully on Sunday in a breakthrough deal with the European Union to avoid U.N. Security Council sanctions.

A Vienna-based diplomat confirmed that the United Nations’ nuclear watchdog agency received the letter from Iran on Sunday evening that contained a “commitment to full suspension of Iran’s uranium enrichment program.”

Details of the deal were unclear Sunday night, but Britain, France and Germany had previously offered Iran a light-water nuclear reactor to generate electricity, help acquiring nuclear fuel and perhaps support for Iran’s bid to join the World Trade Organization in exchange for a full freeze and access to all nuclear sites for the United Nations’ nuclear watchdog agency.

A similar deal brokered by the three European nations last year fell apart after about six months because of lack of agreement over the terms.

The announcement comes 10 days before the board of the International Atomic Energy Agency, the U.N. agency, will meet to decide the next step for Iran. The letter will be included in the report to the board of governors, which is to go out today.

Until Sunday, Iran had rejected the 35-member board’s request in September to suspend enrichment activities as “a confidence-building measure” while the agency continued to investigate whether Iran was using its energy program to develop nuclear weapons.

The EU had warned Iran that without a freeze, the three European nations would back a U.S. call to refer the issue to the U.N. Security Council, which could impose economic sanctions.