Iran’s sole nuclear power plant has undergone an unexplained temporary emergency shutdown, the country’s state TV reported.

An official from the state electric company Tavanir, Gholamali Rakhshanimehr, said on a talk show that aired on Sunday that the Bushehr plant shutdown began on Saturday and would last “for three to four days.” Without elaborating, he said that power outages could result.

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This is the first time Iran has reported an emergency shutdown of the plant in the southern port city of Bushehr. It went online in 2011 with help from Russia. Iran is required to send spent fuel rods from the reactor back to Russia as a nuclear nonproliferation measure.

The report came as top diplomats said that further progress had been made at talks Sunday between Iran and global powers to try to restore a landmark 2015 agreement to contain Iranian nuclear development that was abandoned by the Trump administration. They said it was now up to the governments involved in the negotiations to make political decisions.

Earlier in the day, Tavanir released a statement saying that the Bushehr nuclear plant was being repaired, without offering further details. It said the repair work would take until Friday.

In March, nuclear official Mahmoud Jafari said the plant could stop working since Iran cannot procure parts and equipment for it from Russia due to banking sanctions imposed by the U.S. in 2018.

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Bushehr is fueled by uranium produced in Russia, not Iran, and is monitored by the United Nations’ International Atomic Energy Agency. The IAEA acknowledged being aware of reports about the plant, but declined to comment.

Construction on the plant, on the coast of the northern reaches of the Persian Gulf, began under Iran’s Shah Mohammad Reza Pahlavi in the mid-1970s. After the 1979 Islamic Revolution, the plant was repeatedly targeted in the Iran-Iraq war. Russia later completed construction of the facility.

The plant, which sits near active fault lines and was built to withstand powerful quakes, has been periodically shaken by temblors. There have been no significant earthquakes reported in the area in recent days.

Meanwhile, the European Union on Sunday chaired the final meeting in Vienna of the sixth round of talks between Russia, China, Germany, France, Britain and Iran.

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The nations involved in the negotiations have been trying to resolve the major outstanding issues on how to return the U.S. into the landmark nuclear agreement, which then-President Donald Trump pulled Washington out of unilaterally in 2018. Trump also restored and augmented sanctions to try to force Tehran into renegotiating the pact with more concessions.

The meeting was the first since Iran’s hard-line judiciary chief won a landslide victory in the country’s presidential election last Friday. Some diplomats expressed concern that the election of Iran’s incoming President Ebrahim Raisi could complicate a possible return to the nuclear agreement.