International inspectors report that Iran's stockpile of nuclear fuel has increased about 20 percent over the past 18 months of negotiations, according to The New York Times.
The increase in Iran's stockpile was based on a report issued Friday by the International Atomic Energy Agency, which monitors nuclear programs for the United Nations.
The report also said Iran had stopped producing certain types of highly enriched uranium since January, 2014 and halted work on facilities capable of producing nuclear bombs.
The Times noted that should negotiators finalize a deal before a June 30 deadline, Tehran would have to reduce its stockpile by more than 9 tons within months.
The newspaper also reported that Western officials and experts were unsure how or why Iran's stockpile had increased. Some have speculated it was to give them leverage in talks.
The Obama administration has long maintained that Tehran's nuclear program has been "frozen" as international negotiators work to secure a deal with new limits.
A deal brokered between the U.S., Britain, France, Germany, Russia and China with Iran would lift some sanctions on Iran in exchange for new limits on its nuclear program.
A framework outlined April 2 would force Iran to reduce its nuclear stockpile to 300 kilograms, or about 660 pounds.
Secretary of State John KerryJohn KerryOvernight Energy & Environment — Presented by the League of Conservation Voters — EPA finalizing rule cutting HFCs Overnight Energy & Environment — Presented by the League of Conservation Voters — Senate Finance chair backs budget action on fossil fuel subsidies Kerry: 'We can't get where we need to go' in climate fight if China isn't joining in MORE, who has led U.S. talks to secure a deal, met with his Iranian counterpart, Mohammad Javad Zarif, on Saturday in Geneva.
Kerry cut short his trip and returned to Boston on Monday after a cycling accident in France over the weekend left him with a broken leg.
The State Department maintains the June 30 deadline remains set.
White House press secretary Josh Earnest described the report from international inspectors as just a "snapshot in time" amid ongoing talks.
“There are going to be ebbs and flows in terms of the amount of low-enriched uranium in their stockpile," he said. "The requirement is for them to be at the cap by June 30, and our nuclear experts continue to have confidence that they will meet that requirement."
A State Department official also shrugged off the story's implications.
"There are some real issues, serious ones, we have to resolve in these talks. This just isn't one of them," said Marie Harf, senior advisor for strategic communications.
Harf explained that under a joint plan of action with Iran, which was extended, Tehran's stockpile can fluctuate. She noted Iran had agreed to reduce its stockpile to 300 kilograms.
"How they'll do that is a topic of negotiation, but quite frankly, it's not one of the toughest ones," she said during a daily briefing.
-Updated at 4:50 p.m.