Iranian officials now say they will not agree to ship the bulk of their enriched uranium stockpile abroad, The New York Times reported Sunday night, potentially scuttling a deal over their nuclear program.

“The export of stocks of enriched uranium is not in our program, and we do not intend sending them abroad,” Deputy Foreign Minister Abbas Araqchi reportedly said. “There is no question of sending the stocks abroad.”

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U.S. negotiators have reportedly been working under the assumption that the Iranians would send their enriched uranium to Russia. But with one day left before the talks reach a self-imposed deadline, the report cast into doubt whether the U.S. and Iran would be able to strike a deal that satisfied U.S. concerns about Iran’s ability to pursue a nuclear weapon.

Negotiators are reportedly working with the idea that Iran could dilute its uranium stockpile while keeping it inside the country.

A State Department spokeswoman said Monday morning that “the details in that story actually aren’t accurate.”

“Obviously, the stockpile and what happens to it and how Iran gets rid of it is a key part of this possible agreement that we’re trying to get to,” deputy spokeswoman Marie Harf said on MSNBC’s “Morning Joe.” “But the notion that we had some agreement that in the last 24 hours Iran has backed away from just is factually inaccurate.”

“There’s never been agreement on that. We’ve been talking with them about a couple different ways they could do it, and we’ll see if we can get to agreement in the next 24 hours or so.”

The Obama administration is hoping to reach a deal by Tuesday in part because Congress has pledged to consider imposing new sanctions on Iran should the talks falter. However, Secretary of State John KerryJohn Forbes KerryWarren taps longtime aide as 2020 campaign manager In Virginia, due process should count more than blind team support Trump will give State of Union to sea of opponents MORE has said in the past that an extension of the talks would be possible if the two parties had an outline of a deal.

Harf said that if they failed to reach an accord by the deadline, they would look at a non-diplomatic options for dealing with Iran.

“We know that diplomacy is the best way to handle this — the most durable, gives you the most transparency, things that I think people think are good — but we have other options if we can’t get this done diplomatically, and we’ll see where we are,” she said.

A deal will likely require Iran to freeze its nuclear program for at least 10 years in return for lifting Western sanctions that have hurt its economy.