In a move seen as a defiant step as world powers look to rein in Iran's nuclear program, the county has started installing sophisticated centrifuges at its main uranium enrichment plant, a U.N. nuclear report confirmed on Thursday.
The International Atomic Energy Agency (IAEA) said that 180 of the so-called IR-2m centrifuges and empty centrifuge casings had been hooked up at the plant near the town of Natanz, Reuters reported Thursday. The centrifuges were not yet operating.
The advanced centrifuges are expected to accelerate Iran's ability to process more highly enriched uranium. The West and Israel are fearful that such material could be used to build an atomic weapon.
"This is yet another provocative step by Iran and will only invite further isolation by the international community," said Tommy Vietor, spokesman for the National Security Council. "We continue to believe there is time and space for diplomacy to work, but actions like this undercut the efforts of the international community to resolve its concerns over Iran's nuclear program."
For its part, Iran claims it is only increasing its stockpiles of refined uranium for peaceful purposes — in order to produce energy.
Still, the White House and intelligence officials had been anticipating the report and Iran itself had in fact notified the U.N. nuclear watchdog in January that it intended to take the step.
According to Reuters, the confidential report also said Iran had increased to 367 pounds the amount of uranium refined to a purity of 20 percent. That is a level Tehran says it needs for conversion to reactor fuel. In August 2012, the U.N. watchdog group had reported that Iran had stockpiled 200 pounds of the 20-percent material.
About 530-550 pounds of uranium enriched to a level of 20 percent is required for a single nuclear weapon. That would need to be further refined to about 55 pounds of uranium enriched to a 90 percent purity level, according to the U.N. watchdog.
But the IAEA report also said Iran in December resumed converting some of its more highly enriched uranium to powder that would be used in the production of reactor fuel, Reuters reported. That was seen as an positive step in light of Western concerns.
Israel has warned that it might bomb Iran's nuclear sites as a last resort. In a speech to the U.N. in September, Israeli Prime Minister Benjamin Netanyahu said that with a nuclear armed Iran, no one in the world would be safe.
This week, Israel's UN Ambassador Michael Oren told MSNBC's "Morning Joe" that this summer is the "red line" beyond which Israel would not be confident Iran wasn't secretly reaching the point of no return in its nuclear progress.
But a resumption of conversion to fuel, experts told Reuters, means the Israeli "red line" for action could be postponed.
Next week, The Unites States, Russia and European allies are set to resume negotiations with Iran on its nuclear program. The negotiations will take place in Kazakhstan.
NBC News' Andrea Mitchell and Reuters contributed to this report.