A top Pentagon official said Tuesday that Iran could make the nuclear material for a device in about 12 days if it wanted to do so.

Last week, the International Atomic Energy Agency said its monitors had detected that Iran now had the capability of enriching uranium to close to 84%.

On Tuesday, the IAEA said the capability had actually reached 83.7 percent, which is on the verge of making weapons-grade uranium.

In response to a question from Rep. Jim Banks, R-Ind., at a House Armed Services Committee hearing on Ukraine, Colin Kahl, the Pentagon's top policy official, was asked to describe Iran's nuclear progress since then-President Donald Trump pulled the U.S. out of the Iran nuclear deal, known as the Joint Comprehensive Plan of Action, or JCPOA.

"Iran's nuclear progress since we left the JCPOA has been remarkable," Kahl said.

"Back in 2018, when the previous administration decided to leave the JCPOA, it would have taken Iran about 12 months to produce one bomb's worth of fissile material," said Kahl about Iran's so called "breakout time. "Now it would take about 12 days."

Kahl said he still thinks going back to the deal is better than not having any deal because he said it could "put constraints" on Iran. At the same, he acknowledged that isn't likely, given that efforts to go back to the deal are "on ice" since Iran turned down a U.S. offer last summer.

"Of course, Iran's behavior has changed since then, not the least of which there's support for Russia and Ukraine, which is the subject of the conversation here today," he told lawmakers. "So, I don't think we're on the precipice of reentering the JCPOA."

abc news/ByLuis Martinez