Iran could produce enough weapons-grade uranium to build an atomic weapon within two weeks and has, “in a certain way,” already reached the point of no return in its nuclear program, a former senior International Atomic Energy Association official said Monday.

“I believe that if certain arrangements are done, it could even go down to two weeks. So there are a lot of concerns out there that Iran can hopefully now address, in this new phase, both at the P5+1 [talks between Tehran and six world powers] and with the IAEA,” former IAEA deputy director Olli Heinonen said, confirming a report released last week by the Washington-based Institute for Science and International Security, which stated Iran could muster enough uranium for a bomb by converting all of its 20-percent enriched stockpile within 1 to 1.6 months.

Earlier on Monday, IAEA Director Yukiya Amano met in Vienna with Iranian Deputy Foreign Minister Abbas Araqchi, Tehran’s top nuclear negotiator, ahead of two days of technical talks between Iranian representatives and the UN’s nuclear watchdog. Amano described his meeting as important in addressing “the outstanding issues regarding Iran’s nuclear program.”

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Speaking to journalists on a conference call organized by The Israel Project, Heinonen contrived to sound optimistic and pessimistic at the same time.

“They are forward looking,” he about about the Iranian negotiators. “And I think they have realized that they don’t get away from this situation unless they answer properly the questions raised by the IAEA and concerns raised by the international community. So I’m to a certain degree hopeful. But we have to make sure that everything is covered.”

Asked specifically if Iran had passed the “point of no return” in its nuclear program, Heinonen, today a senior fellow at the Harvard Kennedy School of Government’s Belfer Center for Science and International Affairs, replied, “Yes, in a certain way. But we have to remember what are the capabilities of Iran. People have slightly different definitions of breakout capability.”

In his assessment, which appears to concur with that of Prime Minister Benjamin Netanyahu, a critical level is reached when the Iranians have enriched enough uranium to weapons grade, in the form of hexafluoride gas enrichment, to create a nuclear bomb.

“But you still don’t have a nuclear weapon,” Heinonen added. Preparing the highly enriched uranium for a nuclear bomb would take another month or two, “assuming that someone has all the knowledge.” After that, assembling an actual nuclear weapon that can be delivered with a ballistic missile would take perhaps another year, he said.

Iran continues to install hundreds of new advanced centrifuges every month, drastically reducing the so-called breakout time it would require in order to produce weapons-grade uranium if it decided to do so, he said.

Israel has called for Iran to be stripped of all enrichment capability, saying even low-grade uranium could be made suitable for a nuclear weapon in a short time with enough centrifuges running. “Regarding Iran, we are not impressed by the discussion surrounding the issue of 20% enrichment,” Netanyahu said Sunday, referring to reports that Tehran has been insisting on retaining the ability to enrich uranium to that level. “Its importance is superfluous as a result of the improvements the Iranians have made in the past year, which allow them to jump over the barrier of 20% enrichment and proceed directly from 3.5% enrichment to 90% within weeks, weeks at most.”

Heinonen said he understood Netanyahu’s concerns, because once Iran produces weapons-grade uranium and already has 20% enriched uranium, 90% of the work is already done. It is incorrect to refer to 20% enriched uranium as “medium-enriched uranium,” he said, because “the cup is not half-full or half-empty, it’s a cup 90% full, because you need to do only that tiny, small additional 10% of effort to produce highly enriched uranium,” he said.

Unfortunately, the situation is similar with low-enriched uranium, Heinonen said. “Because once you have produced 3.5% or 5% enriched uranium — Iran now has quite a big stock of seven metric tons of that material — actually you have done something like 60% of the effort you need to do in order to produce weapons-grade uranium.”

With Iran’s current inventory of 20% enriched uranium hexafluoride, he added, “they can turn it into the equivalent of nuclear weapon material in one month’s time. That’s a fact.” If they start with 3.5% enrichment, it would take two months or slightly more, he said.

The international community also has grounds to be concerned over other aspects of Iran’s nuclear ambitions, Heinonen cautioned, since in the past Iran didn’t always disclose all aspects of its nuclear program. “So the question is: Is everything now on the table? Has Iran declared everything, or is there still something the international community doesn’t know?”

Shortly after the Araqchi-Amano meeting Monday, technical and legal experts from Iran and the IAEA were scheduled to begin two days of talks about Iran’s nuclear program. IAEA experts are looking to investigate suspicions that Iran for years worked secretly on developing a nuclear-weapons program.

Representatives of the two sides have already met 11 times since January as the IAEA tries to negotiate access to some of Iran’s nuclear facilities in order to monitor activity within the sites.

The sides are scheduled to hold diplomatic-level meetings in Vienna on November 7 and 8.

The flurry of activity comes amid intensified efforts by the West to curb enrichment in Iran. A meeting in mid-October between Iran and the P5+1 — US, UK, France, Russia, China and Germany — produced cautious optimism that a deal could be reached to rein in Iran’s rogue nuclear program in exchange for eased sanctions.

The optimism came after years of inconclusive meetings. The talks in Geneva were focused on limiting Iranian nuclear programs that can be used both to generate power and make fissile warhead material.

The key elements of the talks are Iran’s uranium enrichment program and its plutonium heavy-water facility. Western nations argue that the 20-percent enriched uranium and the plutonium Iran is producing are not necessary for generating nuclear power and therefore must be halted with all such material removed from the country.

In an effort to pressure Tehran to agree to the demands, a series of sanctions has been enforced on Iran’s oil and financial sectors over the past couple of years. Tehran hopes to negotiate an easing of the sanctions without giving up its enrichment program.

On Sunday, Iranian Parliament Speaker Ali Larijani told China’s Phoenix news network that he believes a deal can be reached within a year, but said Tehran will not halt the program if talks fail.

“The settlement of nuclear issues completely depends on the approaches and if a positive approach rules the negotiations and there exists some seriousness, one can hope for the settlement of issues in less than a year,” Larijani said, according to a report in the Iranian state-run Fars news agency. “If the negotiations fail to yield results, we will continue the present path and approach that we are paving now.”

Iran denies working toward nuclear arms, claiming all its atomic activities are peaceful. While the talks with the IAEA and the P5+1 are formally separate, they are linked by concerns over Iran’s nuclear aspirations, and progress in one may result in advances in the other.

The diplomatic atmosphere between Iran and Western powers improved following the August installation of President Hassan Rouhani, who is considered more moderate than his predecessor Mahmoud Ahmadinejad. During the United Nations General Assembly meetings at the beginning of September, Iranian officials, including Rouhani, held ground-breaking meetings with Western leaders after years of diplomatic severance.

However, Israeli officials maintain that, regardless of its diplomatic overtures to the West, Iran is still hell-bent on achieving nuclear weapons.

Stuart Winer and The Associated Press contributed to this report.