Updated at 8:45 p.m. ET

Iran has announced that it will begin enriching uranium using centrifuges at a controversial and heavily fortified nuclear facility. It's the latest in a series of breaches by Iran following President Trump's decision to abandon an international nuclear deal and impose economic sanctions.

In a televised speech on Tuesday, Iranian President Hassan Rouhani said there are about 1,044 centrifuges at the Fordow nuclear facility. And on Wednesday, even though it is against the terms of the deal, Iran will begin to inject them with a gas containing uranium.

"Once they live up to their commitments, we will stop feeding gas to the centrifuges," Rouhani said, according to a translation from Iran's Press TV. He appeared to be referring to the imposition of sanctions, which were to be lifted under the agreement that came into force in 2016.

U.S. State Department spokesperson Morgan Ortagus said Tuesday that the news comes as "no surprise."

"We have made clear that Iran's expansion of uranium enrichment activities in defiance of key nuclear commitments is a big step in the wrong direction and underscores the continuing challenge Iran poses to international peace and security," Ortagus added.

It's not clear how many centrifuges will be injected with the gas.

Iranian nuclear head Ali Akbar Salehi said the country would be enriching the uranium up to 5% — which is still within the range used for nuclear power reactors. The terms of the deal limited enrichment to 3.67%, and Iran is currently enriching uranium to about 4.5%.

As NPR has reported, weapons-grade uranium is much more highly enriched — to about 90%. "Right now we have enough 20% uranium, but we can produce more as needed," Salehi told the Iranian news agency ISNA, according to Reuters. Iran had a significant amount of 20% uranium, which is used in some research reactors, before the deal was reached.

Experts say the gas infusion isn't expected to dramatically affect Iran's "breakout time" — the time it would take to produce the amount of highly enriched uranium needed to make a bomb.

David Albright, a physicist at the Institute for Science and International Security, told NPR, "I would not think breakout time would be affected very much, at least initially." He says it partially depends on how many centrifuges are injected with gas.

However, he says this violation of Iran's nuclear agreement "is one of the most serious ones and could be perceived as the restart of Iran's nuclear weapons capability."

The Fordow facility has been controversial for years. It is buried inside a mountain and was kept secret until it was discovered in 2009. The nuclear deal called for it to be used as a research facility, according to The Associated Press.

Ariane Tabatabai, a political scientist at the Rand Corp., tells NPR that Iran has kept some of Fordow's centrifuges spinning, which was allowed under the agreement. That was important to Iran's leaders for domestic political reasons.

"It was more of a political, sort of visible, concession that Iran got, which was very important domestically because the supreme leader had said that Iran was not allowed to close any facilities," Tabatabai says.

"What the step seems to be doing is actually taking us back to a position where Iran can once again use the facility for enrichment purposes," she says. "This is a big deal."

Iran has been breaching some aspects of the deal for months. It has previously justified breaches by saying that such actions provide "an opportunity for talks."

Rouhani's announcement puts European countries hoping to keep the nuclear deal intact in a difficult position. As The Associated Press reported, EU spokesperson Maja Kocijancic called on Iran "to reverse such steps without delay and to refrain from any further measures that would undermine the nuclear deal."

NPR's Geoff Brumfiel contributed to this report.

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