Iran Could Produce Nuclear Weapon in Several Months if It Decides to Do So, Mark Milley Says

Iran would need only several months to build a nuclear weapon if Tehran opted to produce a bomb, Gen. Mark Milley, chairman of the Joint Chiefs of Staff, told Congress on Thursday.

Gen. Milley’s assessment provides a significantly shorter estimate for how quickly Tehran could become a nuclear power than other public estimates by Western officials and adds to mounting concern about the advances in Iran’s nuclear program.

“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. Milley said in his opening statement to the House Appropriations Subcommittee on Defense.

That statement echoed recent assessments by U.S. officials that Tehran could produce enough weapons-grade material for a nuclear bomb in a matter of days but then went further by estimating how long the process of turning that material into a weapon might take.

Gen. Milley’s statement was coupled with a warning that the U.S. won’t allow Iran to have a “fielded nuclear weapon.”

“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,” Gen. Milley said.

U.S. intelligence agencies said in February that Tehran isn’t now taking the steps that would be required to turn the fissile material it has acquired into a nuclear bomb.

“To the best of our knowledge, we don’t believe that the Supreme Leader in Iran has yet made a decision to resume the weaponization program that we judge that they suspended or stopped at the end of 2003,” CIA Director William Burns told CBS that month.

Talks on reviving the 2015 Iran nuclear agreement, which the U.S. exited under the Trump administration in 2018, stalled last year.

Iran has always said its nuclear program is for purely peaceful purposes. However, it is the only nonnuclear-weapons country producing 60% highly enriched uranium, and the U.N. atomic agency concluded in 2015 that Tehran had pursued a nuclear-weapons program at least until 2003. Weapons-grade level uranium is considered 90% purity.

In the past, U.S. officials have largely steered clear of public remarks on how long it would take Iran to build a nuclear weapon if it decided to do so. Privately, however, U.S. officials have signaled they believed Tehran could build a nuclear weapon in around a year.

Other western officials have echoed those estimates. In January 2020, former French Foreign Minister Jean-Yves Le Drian said it could take Iran one to two years to build a nuclear weapon. Some Israeli officials have given a similar timeline.

In December, David Albright, a former weapons inspector who is president of the Institute for Science and International Security, said that Iran could produce its first crude nuclear weapon in six months.

However, others believe it could take anywhere between one and three years for Iran to develop a more effective weapon.

“There is no doubt that Iran could produce a nuclear weapons once it had the fissile material, but I think there are huge uncertainties about how quickly they could do it, ” said 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.

“We just don’t know how quickly Iran can restart and finish the research and development work they were doing before 2003,” Mr. Samore added.

Henry Rome, senior fellow at the Washington Institute for Near East Policy, said that a shortened “breakout to bomb” estimate could have consequences for policy makers.

“If the assessment is that the window is a matter of months, not more than a year, it will put more pressure on policymakers to act much more quickly when it comes to deciding on military action,” Mr. Rome said.

Col. Dave Butler, a spokesman for Gen. Milley, declined to elaborate on his assessment to Congress, saying the “chairman’s statement speaks for itself.”

A spokeswoman for the White House’s National Security Council didn’t directly address Gen. Milley’s weapons production estimate.

“The United States is committed to never allowing Iran to acquire a nuclear weapon,” she said. “We believe diplomacy is the best way to achieve that goal, but President Biden has also been clear that we have not removed any option from the table.”

Write to Laurence Norman at laurence.norman@wsj.com and Michael R. Gordon at michael.gordon@wsj.com