BRUSSELS (AFP) - The European Union has informally contacted the incoming Trump administration to clarify "misunderstanding" about the Iran nuclear deal which he has threated to scrap, an EU diplomatic source said Tuesday (Jan 17).

EU foreign affairs head Federica Mogherini on Monday insisted the bloc would stand by the accord - which she helped negotiate - because it showed that diplomacy worked and served Europe's security needs.

US President-elect Donald Trump has blasted the agreement as "one of the dumbest deals I have ever seen" and warned it will not stop Tehran getting atomic weapons.

The EU diplomatic source, who asked not to be named, said the contacts were made to explain the value of the accord.

"Some informal outreach was done to the new US administration to explain the added value of the deal," the source said.

"There has been a lot of misunderstanding out there ... It is a multilateral agreement; if one side steps away from it, the others can do the same."

The source said the EU was determined to stick with the accord and was "working very much hand in hand with China and Russia on this."

"We see this deal as very important, as having averted a potential major crisis in a region running high with tensions," the source added.

Under the hard-won accord, Tehran agreed to rein in its nuclear programme in return for an easing of punishing Western economic sanctions.

US President Barack Obama hailed the accord as one of his major achievements, preventing Iran getting nuclear weapons without having to go to war.