Story highlights The diplomats said the deal is in the national security interests of their countries, the Middle East and the world

Under US law, the President has to certify to Congress every 90 days that Iran is complying with the deal

Washington (CNN) European ambassadors to the US mounted a united defense of the Iran nuclear deal as Washington signals it may walk away from the pact.

Envoys from the European Union, Germany, France and Britain laid out their arguments, returning frequently to their central point that the deal is working and Iran is complying with the agreement reached in July 2015 and implemented in January 2016.

The diplomats said the deal is in the national security interests of their countries, the Middle East and the world. They said a decision to walk away would undermine Western credibility, particularly with North Korea. And while they're happy to discuss Iran's behavior outside of the nuclear deal, they said the pact itself is not open for renegotiation.

"We don't think it will be possible to renegotiate" the Joint Comprehensive Plan of Action, said German Ambassador Peter Wittig, who added that his country saw no practical way to do so.

Other parties to the deal are adamant that it won't happen, French Ambassador Gerard Araud told the audience at the Atlantic Council event where the envoys spoke. At the UN General Assembly, during a meeting last week of all parties to JCPOA, he said, "there was a very clear message" from Iran, China and Russia "saying no way, there won't be any re-opening of the agreement, the agreement is working as it is," Araud said.

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