This Oct. 27, 2004 file photo shows the interior of the Arak heavy water production facility in Arak, 360 kms southwest of Tehran.

Nuclear technicians have finished removing the core of the Iran’s only nuclear heavy water reactor as part of Tehran’s obligations under its nuclear deal with world powers, Iranian state television reported Thursday.

The removal of the core of the nearly completed Arak reactor is a key step before crippling international sanctions on Iran are lifted. The work must still be verified by outside experts.

Under the deal reached last summer, the heavy-water reactor is to be re-engineered so that it produces only minute amounts of plutonium, like enriched uranium a potential pathway to nuclear arms. That involves exchanging the core and other major modifications.

The spokesman for Iran’s atomic department, Behrouz Kamalvandi, announced the completion of the work on the Arak reactor on Thursday.

“About an hour age, our job was finished,” he said. State TV reported that the holes left after the core was removed have been filled with concrete. International inspectors will now verify the job and will send their report to the International Atomic Energy Agency, Kamalvandi said.

The core itself would be kept as a symbol of Iran’s nuclear achievements, he added.

On Wednesday, US officials said Iran could comply with last summer’s nuclear deal as early as Friday, requiring the United States and other nations to immediately suspend billions of dollars’ worth of economic sanctions on the Islamic Republic.

In Vienna, a senior diplomat from one of the six countries that cut the deal with Iran said Wednesday that it would be formally declared implemented — most probably on Friday. The official and diplomat spoke on condition of anonymity because they were not authorized to discuss the matter publicly.

Zarean, the Iranian deputy nuclear chief, also said Tuesday that once modifications at the plant are done are done and Arak goes online, Iran hopes to export excess heavy water produced there to the US through a third country, for uses in research. He added that Savannah River National Laboratory near Jackson, South Carolina, has recently certified high purity of heavy water produced by Iran.

Iran is still expected to produce some 20 metric tons (22 tons) of heavy water at Arak a year. It has said it would domestically consume about 6 tons for medical isotopes and is looking to export the rest.

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