Intelligence agencies and outside experts do so, and their reading of the report on Tuesday appeared clear: In the aftermath of Mr. Trump’s withdrawal from the Obama-era agreement, Iran now has a pathway to a bomb, and it is slowly reconstituting its fuel inventory.

Whether Iran decides to follow that path is unclear.

“Everything we are doing is reversible,” Mohammad Javad Zarif, Iran’s foreign minister, said at the Munich Security Conference last month. “We have always said we are not interested in building nuclear weapons.”

Some of the facilities the agency has demanded access to in Iran, mostly to conduct environmental tests that could reveal the presence of nuclear materials, came to the world’s attention in 2018 after Israeli agents stole a trove of historical materials about the Iranian nuclear program. Since then, Israel has doled out some of the findings to reporters, experts and the IAEA.

David Albright, the president of the Institute for Science and International Security, a nonprofit in Washington that tracks nuclear proliferation, said in an interview that if Iran did race for a bomb, it might need another three to four months to turn the newly revealed amount of uranium into the highly enriched material at the heart of a nuclear warhead.

“It’s worrisome,” he said. “We didn’t expect Iran to be at the 1,000-kilogram mark. I think people are a little surprised at the magnitude of the number. I’m sure it sent a shiver through the international community.”

Both the Obama and Trump administrations saw the Iran deal as keeping Tehran a year or more away from getting enough highly enriched uranium to fashion a single warhead — what international inspectors call “a significant quantity.”

That amount is defined as 25 kilograms, or 55 pounds, of uranium highly enriched in the element’s rare 235 isotope — the atoms of which can split apart in powerful bursts of nuclear energy. A sphere of 55 pounds is said to be about the size of a small melon.