Iran would be only months away from building a nuclear weapon if it opted to produce a bomb, according a top U.S. military official. 

"From the time of an Iranian decision … Iran could produce fissile material for a nuclear weapon in less than two weeks and would only take several more months to produce an actual nuclear weapon," Gen. Mark Milley, chairman of the Joint Chiefs of Staff, told Congress Thursday.

Milley presented a much shorter timeline than officials previously have when discussing Iran’s nuclear capabilities. 

He added that the U.S. won’t allow Iran to have a "fielded nuclear weapon."

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"We, the United States military, have developed multiple options for our national leadership to consider if or when Iran ever decides to develop an actual nuclear weapon," Milley said.

Officials remain concerned about Iran’s nuclear capabilities after attempts to revive the Joint Comprehensive Plan of Action, known as the Iran Nuclear Deal, which the U.S. withdrew from during the Trump administration in 2018. 

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Unnamed senior diplomats told Bloomberg in February Iran has accumulated uranium enriched to 84% purity, a concentration 6% below what’s needed for a weapon, marking the highest levels found by inspectors in Iran to date.

Iran had previously told the International Atomic Energy Agency (IAEA) that its centrifuges were configured to enrich uranium to a 60% level of purity.

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It remains unclear whether the material was intentionally produced or it was an unintentional accumulation within the centrifuges used to separate the isotopes.

The timeline to create a nuclear weapon remains unclear, with some experts believing it could take between six months and three years, according to The Wall Street Journal. 

Gary Samore, the director of the Crown Center for Middle East Studies at Brandeis University and a former White House official during the Obama administration, told the Journal no one can tell "how quickly Iran can restart and finish the research and development work they were doing before 2003." 

Col. Dave Butler, a spokesman for Gen. Milley, declined to elaborate on his assessment to Congress, telling the Journal that the "chairman’s statement speaks for itself."

Fox News Digital’s Bradford Betz contributed to this report.