The foreign ministers of France, Germany and the United Kingdom , also known as the E3, have submitted a letter of intent to the United Nations  confirming their plans to reinstate sanctions on Iran if the Islamic Republic does not allow international inspectors access to its controversial nuclear sites.

The letter, seen by news agency AFP and the Financial Times newspaper, was addressed to UN Secretary-General Antonio Guterres as well as the UN Security Council.

In it, the E3 representatives said that their countries — all of which were signatories to the 2015 Joint Comprehensive Plan of Action (JCPOA) or "Iran nuclear deal" alongside China, Russia and the United States  — "committed to use all diplomatic tools at our disposal to ensure Iran does not develop a nuclear weapon" if Tehran does not seek to arrive at a diplomatic solution to a current impasse by the end of August.

Is Iran developing nuclear weapons?

The three cited so-called "snapback mechanisms" that allow sanctions to be reinstated if Iran fails to comply with the conditions of the JCPOA, which sought to end Tehran's nuclear program.

Critics say Iran's religious leaders aim to create a nuclear weapon, something Tehran has steadfastly denied for years despite being unable to provide reasons for producing large amounts of uranium enriched far beyond grades needed for civilian purposes.

The JCPOA is set for renewal or expiration in October, in their letter, the E3 wrote, "We have made clear that if Iran is not willing to reach a diplomatic solution before the end of August 2025, or does not seize the opportunity of an extension, E3 are prepared to trigger the snapback mechanism."

Manouchehr Mottaki, Iran's former foreign minister and now a parliamentarian, told Iranian media that the country is prepared to withdraw from the nuclear Non-Proliferation Treaty (NPT) — which aims to prevent the spread of nuclear weapons — if international sanctions are reintroduced.

Why has Iran denied access to its nuclear sites?

One of the main criticisms of Iran's behavior is its refusal to allow inspectors from the International Atomic Energy Agency (IAEA) into its facilities. Iran has strictly limited access to its sites since 2018, when US President Donald Trump withdrew the US from the JCPOA.

Tehran later shut out IAEA inspectors when Israel began a 12-day assault mainly on Iranian nuclear facilities and the United States — despite having conducted prior "useful" direct talks with Tehran — joined in by conducting massive bomb strikes on Iranian nuclear sites.

The Tuesday letter states, "The E3 remain fully committed to a diplomatic resolution to the crisis caused by Iran's nuclear program and will continue to engage with a view to reaching a negotiated solution."

"We are equally ready, and have unambiguous legal grounds, to notify the significant non-performance of JCPOA commitments by Iran ... thereby triggering the snapback mechanism, should no satisfactory solution be reached by the end of August 2025."

The E3 warning came on the heels of face-to-face meetings with Iranian counterparts last month in Istanbul, Turkey. Those talks, the first to take place after the Israeli and US attacks, were described as "serious, frank and detailed."

Despite having shut out IAEA inspectors, Tehran said the UN agency's boss, Rafael Mariano Grossi, was expected to visit Iran for negotiations on a new cooperation deal.

Iran has claimed that JCPOA signatories have no legal right to reapply sanctions, a claim scoffed at by E3 ministers as "unfounded."

In refuting Iran's claim, E3 foreign ministers wrote that signatories are, "clearly and unambiguously legally justified in using relevant provisions" of UN resolutions "to trigger UN snapback to reinstate UNSC resolutions against Iran which would prohibit enrichment and re-impose UN sanctions."

Edited by: Sean Sinico