ISTANBUL

The US strikes last month heavily damaged one Iranian nuclear site, while the other two suffered limited damage and could resume enrichment within months, according to a recent US assessment of the destruction caused by the military operation, five current and former US officials familiar with the assessment told NBC News.

The operation, conducted under the Trump administration, targeted Iran’s nuclear facilities at Fordo, Natanz, and Isfahan.

The attack on Fordo was successful in setting back Iran’s enrichment capabilities there by as much as two years, according to two current officials.​​​​​​​

The two other sites targeted sustained less damage and may have been degraded only to the point where nuclear enrichment could resume within several months if Iran chooses to do so.

The assessment was delivered in recent days to some US lawmakers, Department of Defense officials, and allied governments.

NBC News also learned that US Central Command had planned a larger strike on Iran targeting three more sites over several weeks, not just one night, according to a current and two former US officials. President Trump was briefed, but he rejected it, preferring to avoid deeper conflicts and high casualties, one of the current officials and one of the former officials said.

“We were willing to go all the way in our options, but the president did not want to,” one of the sources with knowledge of the plan said.

On June 22, US B-2 bombers dropped 14 GBU-57 Massive Ordnance Penetrator (MOP) bombs, also known as bunker busters, on Iran’s Fordo and Natanz nuclear sites, and dozens of submarine-based Tomahawk cruise missiles were fired at its nuclear facility at Isfahan as part of Washington’s campaign against Iran’s nuclear program.

A sixth round of talks between the US and Iran was scheduled for June 15, but Israel launched airstrikes on Iranian military, nuclear, and civilian sites on June 13.​​​​​​​

A 12-day conflict between Israel and Iran ended with a US-sponsored ceasefire that took effect on June 24.