World powers on Wednesday (April 14) expressed "grave concern" over Iran's announcement it would move to boost uranium enrichment up to 60%.
The step would bring Iran closer to the 90 percent purity threshold for military use and shorten its potential "breakout time" to build an atomic bomb.
Britain, France and Germany said the announcement was "particularly regrettable" at a time when talks have resumed in Vienna, including with the United States, to revive the 2015 nuclear deal, known as the Joint Comprehensive Plan of Action (JCPOA).
The White House said Tuesday it remains committed to the talks despite Tehran's "provocative" statement that it will ramp up uranium enrichment.
"We are certainly concerned about these provocative announcements," President Joe Biden's press secretary, Jen Psaki, told reporters.
"We believe that the diplomatic path is the only path forward here and that having a discussion, even indirect, is the best way to come to a resolution."
The six countries that negotiated the JCPOA with Iran should be "unified in rejecting" Iran's threat to accelerate uranium enrichment, Psaki said.
Violations at Natanz
Iran's announcement came after an explosion followed by power failure occurred at its Natanz uranium enrichment facility on Sunday (April 11).
No one has accepted responsibility for the attack, but European powers have said they reject "all escalatory measures by any actor".
The Natanz facility's blackout, caused by a deliberately planned explosion, has disabled Iran's uranium enrichment, preventing it from enriching uranium for months, the New York Times reported.
Iranian authorities have offered contradictory narratives about Sunday's incident, and released no post-incident photos or video footage.
Iranian government spokesman Ali Rabiei said Tuesday the "sabotage occurred in a duct of power cables leading to the centrifuge machines which caused damage to this system".
Natanz is one of the primary facilities where Iran continues to actively breach the terms of the 2015 nuclear deal by enriching uranium at higher purity levels than agreed upon and stockpiling it.
Enriching uranium up to 60% would be a further break with the terms of the JCPOA.
Tehran has been producing uranium enriched up to 20% since January in violation of the deal, and is advancing research on uranium metal production, aiming to provide advanced fuel for a research reactor in Tehran.
The Sunday incident took place less than 24 hours after Iran announced it had brought into service or begun testing several hundred centrifuges forbidden under the 2015 agreement.
Alongside the new centrifuges, Iranian President Hassan Rouhani had on Saturday also inaugurated a new centrifuge assembly factory at Natanz.