A new report by the UN’s nuclear watchdog that Iran has installed and activated nearly 200 advanced centrifuges proves the Islamic Republic is steadily working its way toward the red line at which it couldn’t be stopped from obtaining nuclear weapons, Prime Minister Benjamin Netanyahu said Thursday.

“This is a very grave report which proves that Iran is continuing to make rapid progress toward the red line. Today, Iran is close than ever to achieving enriched material for a nuclear bomb,” a statement by the Prime Minister’s Office said, adding the need to prevent Iran from attaining nuclear weapons would be the first subject discussed with US President Barack Obama on his upcoming visit.

UN nuclear inspectors have counted nearly 200 advanced machines fully or partially installed at Iran’s main uranium enrichment site, an International Atomic Energy Agency report leaked to the media Thursday stated, confirming diplomats’ accounts that Tehran has begun a major upgrade of a program that can be used in the making of atomic arms.

The US also reacted harshly to the report, with State Department spokesperson Victoria Nuland calling the revelation disturbing and “yet another provocative step” from Iran.

“The installation of new advanced centrifuges would be a further escalation, and a continuing violation of Iran’s obligations under the relevant UN Security Coucil resolution and IAEA board resolutions,” she said.

White House spokesperson Jay Carney said there was still an opportunity for Iran and the West to solve things diplomatically, but stressed “that window will not remain open indefinitely.”

Iran denies it wants such weapons and says it is enriching only to make reactor fuel and for scientific and medical purposes under international law specifically allowing such activities. But because it hid its enrichment program — and other nuclear activities — for decades, many countries fear that it ultimately wants to enrich to weapons-grade level, suitable for arming nuclear warheads.

Iran announced last month that it planned to upgrade its Natanz enrichment facility, then said earlier this month that it had started doing so.

On Wednesday, diplomats told The Associated Press that upward of 100 enriching centrifuges had already been installed.

However, the IAEA report, circulated Thursday to the 35-nation agency board, was the first independent and on-record confirmation that the work had begun and was advancing. The confidential IAEA report, which was leaked to news media, said IAEA inspectors saw 180 of the high-tech IR 2m centrifuges fully or partially mounted at Natanz during a February 6 inspection tour.

The advance is significant both in terms of technology and timing. The IR-2m centrifuges can enrich three to five times faster than the outmoded machines now being used at Natanz. For nations fearing that Iran may want to make nuclear arms that means a quicker way of getting there, should Tehran actually break out of its present peaceful enrichment program to openly work on a weapon.

The start of the upgrade is also of concern to six world powers that are preparing to open talks with Iran about its nuclear program on Tuesday in Kazakhstan. They want Tehran to cut back on enrichment, saying the installation of new machines instead sends the signal that the Islamic Republic is expanding that activity.

“It’s very hard for the international community to understand what Iran is doing, when it claims that all of this is peaceful,” Nuland told reporters.

Both she and the British Foreign Office suggested that the centrifuge installations would additionally burden already difficult nuclear negotiations with Tehran, which have led to lack of substantial progress in previous rounds. While the US and its Western allies want a rollback of enrichment before any easing of sanctions crippling Iran’s oil sales and financial transactions, Tehran has refused to even consider making a move before some sanctions are removed.

Nuland said the move on the centrifuges “doesn’t make it any easier to get where we want to go,” while the Foreign Office, in a separate statement, said the timing “concerns and disappoints us.”

It was unclear, however, how quickly Iran would proceed with the centrifuge upgrade. It hinted last month that it planned to install more than 3,000 of the new machines, and former IAEA Deputy Director General Olli Heinonen has told the AP that Tehran could do that within nine months, assuming it has the components to make them.

But a senior diplomat who is familiar with the report said the agency could not tell whether Iran did in fact possess enough centrifuges — or the raw materials to make them — to reach that goal any time soon. He said the next few months will be crucial to establishing how many machines will be installed and in what time frame. The diplomat demanded anonymity because he was not authorized to comment.

The IAEA report noted that other developments reflecting Iran’s determination to expand enrichment. It said that Tehran had installed 2,255 of its mainstay IR-1 centrifuges since the last report on November 16, bringing the total to 12,699 — although not all were operating.

David Albright, whose Institute for Science and International Security is often consulted by the US government on proliferation issues, said that at that pace “Iran is installing the IR-1 centrifuge at a faster-than expected rate.”

The report also said the number of other advanced centrifuge models being tested at an R&D site at Natanz separate from its enrichment plant had substantially increased to more than 300 as of this month.

While moving to increase the potency of its enrichment program, however, Tehran also has recently resumed converting some of its higher-level enriched uranium at into reactor fuel plates after suspending the activity last year. That is likely to provide some reassurance to nations concerned about Iran’s nuclear aims because the plates are difficult to reconvert back into weapons usable material.

About 700 of the old machines at Fordo — a site separate from Natanz — are churning out higher-enriched material that is still below — but just a technical step away — from weapons-grade uranium. Iran says it needs that higher-enriched level to fuel a research reactor.

With higher-enriched uranium their immediate concern, the six powers’ main demand during the talks on Tuesday in Kazakhstan is suspension of enrichment at Fordo.

About 250 kilograms — 550 pounds — of that higher-enriched uranium is considered to be the standard amount needed to make 25 kilograms, or 55 pounds, of weapons grade uranium.

The IAEA report noted that — with the amount converted subtracted from its present stockpile — Iran now had close to 170 kilograms (375 pounds) of 20 percent enriched uranium. That’s 15 kilograms (33 pounds) more than in November but still well below the amount needed for a weapon.