A preliminary classified U.S. report says the American bombing of Iran’s nuclear sites sealed off the entrances to two of the facilities but did not collapse their underground buildings, according to officials familiar with the findings.

The early findings conclude that the strikes over the weekend set back Iran’s nuclear program by only a few months, the officials said.

Before the attack, U.S. intelligence agencies had said that if Iran tried to rush to making a bomb, it would take about three months. After the U.S. bombing run and days of attacks by the Israeli Air Force, the report by the Defense Intelligence Agency estimated that the program was delayed less than six months.

Former officials said that any rushed effort by Iran to get a bomb would be to develop a relatively small and crude device. A miniaturized warhead would be far more difficult to produce, and it is not clear how much damage to that more advanced research has taken place.

The findings suggest that President Trump’s statement that Iran’s nuclear facilities were obliterated was overstated, at least based on the initial damage assessment. Congress had been set to be briefed on the strike on Tuesday, and lawmakers were expected to ask about the findings of the assessment, but the session was postponed. Senators are now set be briefed on Thursday.

The report also said much of Iran’s stockpile of enriched uranium was moved before the strikes, which destroyed little of the nuclear material. Some of that may have been moved to secret nuclear sites maintained by Iran.

Some Israeli officials said they also believe that Iran has maintained small covert enrichment facilities that were built so the Iranian government could continue its nuclear program in the event of an attack on the larger facilities.

But the Defense Intelligence Agency report indicates that the sites were not damaged as much as some administration officials had hoped, and that Iran retains control of almost all of its nuclear material, meaning if it decides to make a nuclear weapon it might still be able to do so relatively quickly.hy Do Yemeni Coffeehouses Seem to Be Everywhere Lately?

Officials interviewed for this article spoke on the condition of anonymity because the findings of the report remain classified.

The White House took issue with the assessment. Karoline Leavitt, a White House spokeswoman, said it was “flat-out wrong.”

“The leaking of this alleged assessment is a clear attempt to demean President Trump, and discredit the brave fighter pilots who conducted a perfectly executed mission to obliterate Iran’s nuclear program,” she said in a statement. “Everyone knows what happens when you drop 14 30,000-pound bombs perfectly on their targets: total obliteration.”

Elements of the intelligence report were reported earlier by CNN.

The strikes badly damaged the electrical system at Fordo, which is housed deep inside a mountain to shield it from attacks, officials said. It is not clear how long it will take Iran to gain access to the underground buildings and then repair the electrical systems and reinstall equipment that was moved.

Initial Israeli damage assessments have also raised questions of the effectiveness of the strikes. Israeli defense officials said they have also collected evidence that the underground facilities at Fordo were not destroyed.

Before the strike, the U.S. military gave officials a range of possibilities for how much the attack could set back the Iranian program. Those ranged from a few months on the low end to years on the higher end.

Some officials cautioned that such estimates are imprecise, and that it is impossible to know how long Iran would exactly take to rebuild, if it chose to do so.

Mr. Trump has declared that B-2 bombing raids and Navy Tomahawk missile strikes “obliterated” the three Iranian nuclear sites, an assertion that Defense Secretary Pete Hegseth repeated at a Pentagon news conference on Sunday.

But Gen. Dan Caine, the chairman of the Joint Chiefs of Staff, has been more careful in describing the attack’s effects.

The final battle damage assessment for the military operation against Iran, General Caine said on Sunday, standing next to Mr. Hegseth, was still to come. He said the initial assessment showed that all three of the Iranian nuclear sites that were struck “sustained severe damage and destruction.”

At a Senate hearing on Monday, Democrats also struck a more cautionary note in challenging Mr. Trump’s assessment.

“We still await final battle damage assessments,” said Senator Jack Reed of Rhode Island, the senior Democrat on the Armed Services Committee.

Military officials had said that to do more significant damage to the underground sites, they would have to be hit with multiple strikes. But Mr. Trump announced he would stop the strikes after approving the first wave.

U.S. intelligence agencies had concluded before the strikes that Iran had not made the decision to make a nuclear weapon, but possessed enough enriched uranium that if it decided to make a bomb, it could do so relatively quickly.

While intelligence officials had predicted that a strike on Fordo or other nuclear facilities by the United States could prompt Iran to make a bomb, U.S. officials said they do not know yet if Iran would do so.

Representatives of the Defense Intelligence Agency did not respond to requests for comment