One of the three nuclear enrichment sites in Iran struck by the United States last month was mostly destroyed, setting work there back significantly. But the two others were not as badly damaged and may have been degraded only to a point where nuclear enrichment could resume in the next several months if Iran wants it to, according to a recent U.S. assessment of the destruction caused by the military operation, five current and former U.S. officials familiar with the assessment told NBC News.

The assessment, part of the Trump administration’s ongoing efforts to determine the status of Iran’s nuclear program since the facilities were struck, was briefed to some U.S. lawmakers, Defense Department officials and allied countries in recent days, four of those people said.

Iran recently threatened to raise uranium enrichment to weapons-grade levels and exit the Nuclear Non-Proliferation Treaty (NPT) if Western powers move forward with reimposing United Nations sanctions.

Secretary of State Marco Rubio and the foreign ministers of France, Germany, and the United Kingdom agreed in a phone call Monday to set an August deadline for a nuclear agreement.

If no deal is reached by then, the three European powers plan to trigger the UN “snapback” mechanism, which would automatically reinstate global sanctions on Iran’s arms trade, banking sector, and nuclear program.

The possible reactivation of UN snapback sanctions threatens to dismantle the 2015 Joint Comprehensive Plan of Action (JCPOA) and push Iran toward enriching uranium to weapons-grade levels of 90 percent. This crisis has deep roots in the U.S. withdrawal from the deal in 2018 under President Donald Trump, which led Iran to reduce compliance and expand its nuclear program.