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More recently, the U.S., the European Union and other Western allies have either tightened up their own sanctions or rapidly put new penalties in place striking at the heart of Iran’s oil exports lifeline and its financial system.

The most recent squeeze on Iran was announced Friday, when SWIFT, a financial clearinghouse used by virtually every country and major corporation in the world, agreed to shut out the Islamic Republic from its network.

Diplomats say the choke-holds are being applied in part to persuade Israel to hold off on potential military strikes on Iranian nuclear facilities — among them Fordo, a main Israeli concern because it is dug deep into a mountain and could be impervious to the most powerful bunker busting bombs.

Diplomats told the AP earlier this month that Iran had added two new series or cascades of old-generation IR-1 centrifuges to its Fordo operation, meaning 348 centrifuges were now operating in four cascades.

Olli Heinonen, who retired last year as the IAEA’s chief Iran inspector, recently estimated that these machines, and two other cascades at Natanz can produce around 15 kilograms (more than 30 pounds) of 20-percent enriched uranium a month, using Iran’s tons of low-enriched uranium as feedstock.

The low and higher enriched uranium now being produced “provides the basic material needed to produce four to five nuclear weapons,” Heinonen said.

But he suggested “an altogether different scenario” — a much quicker pace of enrichment to levels easily turned into weapons-capable uranium if Iran starts using newer, more powerful centrifuges at Fordo. That, said the diplomats, is exactly what Iran appears to be on the verge of doing by finishing preparatory work recently for new centrifuge installations.

Fordo, which can house 3,000 centrifuges, was confidentially revealed to the IAEA by Iran in 2009, just days before the U.S. and Britain jointly announced its existence.

Iran announced last year that it would move its 20-percent uranium production to Fordo from Natanz and sharply boost capacity. It started making higher grade material two years ago saying it needed it to fuel a research reactor.

But the U.S. and others question the rationale, pointing out that Iran rejected offers of foreign fuel supplies for that reactor and is making more of the higher-enriched material than that small reactor needs.