VIENNA A U.S. think-tank said Iran may have violated last year's interim nuclear deal with world powers by stepping up efforts to develop a machine that could enrich uranium faster, but other experts said they saw no breach.
Iran's development of advanced enrichment centrifuges is sensitive because, if successful, it could enable the country to produce potential nuclear bomb material at a rate several times that of the decades-old model now in use.
Western officials were not immediately available to comment on the allegation by the Washington-based Institute for Science and International Security (ISIS), which closely tracks Iran's nuclear program. There was no immediate comment from Tehran.
ISIS, whose founder David Albright often briefs U.S. lawmakers and others on nuclear proliferation issues, cited a finding in a new report by the International Atomic Energy Agency (IAEA) about Iran.
The confidential document, issued to IAEA member states on Friday, said that since the U.N. agency's previous report in September Iran had "intermittently" been feeding natural uranium gas into a single so-called IR-5 centrifuge at a research facility.
The IR-5 is one of several new models that Iran has been seeking to develop to replace the erratic, 1970s vintage IR-1 centrifuge that it now uses to produce refined uranium.
Unlike other advanced models under development -- IR-2m, IR-4 and IR-6 -- at a research site at its Natanz enrichment plant, Iran had until now not fed the IR-5 with uranium gas.
"Iran may have violated (the interim accord) by starting to feed (natural uranium gas) into one of its advanced centrifuges, namely the IR-5 centrifuge," ISIS said in an analysis.
But the Washington-based Arms Control Association, a research and advocacy group, said it saw no violation, adding that "no enriched uranium is being withdrawn from the machine".
Jofi Joseph, a former director for non-proliferation on the White House National Security Council staff, also said Iran had not violated the agreement. "That would only occur if Iran introduced a brand new centrifuge model to the facility and began feeding it uranium," he wrote in an email.
Iran says it produces low-enriched uranium to make fuel for nuclear power plants. But if processed much further, refined uranium could be turned into the explosive core of a bomb, which the West fears may be the country's latent goal.
Tehran denies looking to build nuclear weapons.
Under last year's deal with the United States, Russia, China, France, Germany and Britain, Iran can continue its "current enrichment R&D (research and development) practices", language that implies it should not expand them. The text of the publicly released agreement did not elaborate on this point, potentially leaving it open for interpretation.
It was one of the thorniest issues to resolve in the negotiations on the temporary accord, which was designed to buy time for talks on a permanent settlement by a Nov. 24 deadline. It is expected to be a key issue also in any long-term deal.
(Reporting by Fredrik Dahl; Editing by Mark Heinrich and Dominic Evans)