For more than a decade, we – Europeans, Americans, and the international community – have feared the imminent threat of a nuclear-armed Iran. To counter this threat and make the Middle East a safer place, the international community came together, using the might of diplomatic negotiations and the force of sanctions, agreed by most of the major economic powers.

After 13 years of joint diplomatic effort, we reached a major breakthrough and signed the Joint Comprehensive Plan of Action (JCPOA), an agreement between Iran, France, the UK, Germany, the US, China, and Russia, regarding Tehran‘s nuclear programme. With that, we were able to impose unprecedented scrutiny on the Iranian nuclear programme, dismantle most of their nuclear enrichment facilities, and drastically reduce the danger of a nuclear arms race. Not a drop of blood was spilt. Furthermore, these controls will not cease after the 10 years of the JCPOA: Iran will continue to be subject to the strict controls prescribed by the nuclear non-proliferation treaty, which will continue to limit enrichment.

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The only reason we were able to achieve this breakthrough is that we stood together. Together, Europeans and Americans have proved that a strong and united transatlantic partnership can bring about a coalition extending to Russia and China, endorsed by the international community.

But this coalition is now at risk, as the US government moves towards abandoning the JCPOA without any evidence of Iran not fulfilling its obligations. The short-term effect of this abandonment would be the end of controls on Iran‘s nuclear programme, resulting in another source of devastating conflict in the Middle East and beyond. The long-term risk is even more serious: lasting damage to our credibility as international partners in negotiation and, more generally, to diplomacy as a tool to achieve peace and ensure security. Abandoning the deal would diminish the value of any promises or threats made by our countries.

Our credibility is all the more urgently needed when we look at the instability in many parts of the world today. With regards to Iran it is an essential ingredient in our much-needed efforts to curb the country’s aggressive regional and domestic policy. As much as we share the concerns expressed by many about Iran’s behaviour, we are deeply convinced that these issues must be treated separately (as we are doing already) – and not within the context of the JCPOA.

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It is in the US and Europe’s interest to prevent nuclear proliferation in a volatile region, and to maintain the transatlantic partnership as a reliable and credible driving force of world politics. We are open to dialogue on the best ways to tackle these challenges together. But let us be clear: if the deal breaks down, it will be well-nigh impossible to assemble another grand coalition built around sanctions against Iran. We must preserve what took us a decade to achieve and has proved to be effective.

Building coalitions and winning consensus is one of our main tasks as members of our respective parliaments. We therefore urge you to stand by the coalition we have formed to keep Iran‘s nuclear threat at bay. This would not only be a powerful sign of the durability of our transatlantic partnership, but also a message to the Iranian people.

Together, let’s keep the JCPOA alive and protect the fruits of successful diplomacy.

• Richard Bacon is an MP and chair of the all-party parliamentary group for Iran, Omid Nouripour is a Green member of the Bundestag and Delphine O is a member of the Assemblée nationale in France. More than 300 other parliamentarians from the three countries signed this letter