VIENNA, Austria – Iran on Sunday agreed to halt its uranium enrichment activities, opening the way for the United Nations’ nuclear watchdog agency to sign the deal when it reconvenes here today, diplomats said.

The deal with three major European nations virtually assured Iran that it would not be referred to the U.N. Security Council, which could impose sanctions.

Diplomats from the European Union and elsewhere said on condition of anonymity that the International Atomic Energy Agency received a letter from Iran containing a pledge not to test 20 centrifuges during the freeze it agreed to Nov. 7 during negotiations with Britain, France and Germany, who were working on behalf of the European Union.

A senior diplomat with nuclear expertise said the Iranian pledge appeared to contain no pitfalls and seemed to meet the European demands for full suspension.

The agency had awaited a formal withdrawal of Iran’s demand to operate 20 centrifuges in defiance of its earlier agreement to halt all enrichment-related programs. Centrifuges are used to enrich uranium for power generation or, if the uranium is highly enriched, for nuclear weapons.

Britain, France and Germany had written an original draft resolution for the agency board, specifying Iranian commitments to halt nuclear enrichment and the agency’s supervision of its program. The agreement stipulated no deadline or penalty for noncompliance.

But Iran had insisted on a further softening of the language to reflect, among other issues, the voluntary nature of the suspension.

Under the agreement, the 20 centrifuges Iran had previously wanted exempted would not be placed under IAEA seals but monitored by cameras, diplomats said.

The United States maintains that Iran is seeking to develop nuclear weapons under the guise of a civilian energy program.

Agency chief Mohamed ElBaradei’s report to the board last week stated that all declared Iranian nuclear materials had been accounted for, although he acknowledged that the agency could not rule out a covert weapons program.