The three European powers noted that the decision does not mean they are joining in US President Donald Trump's "maximum pressure" campaign against Iran - leaving a door open for diplomacy. This month it said it would abandon limits on its production of enriched uranium, a step the Europeans said was likely to force them to respond.
Josep Borrell, the European Union's foreign policy chief, said the aim of the dispute mechanism was not to re-impose sanctions, but "to find a solution for the return to full compliance" with the deal, which was also signed by Russian Federation and China.
In an apparent bid to keep the door open for diplomacy, the three European signatories - known as the E3 - said they were not joining the United States campaign to implement "maximum pressure" against Iran.
Activating the mechanism - which is only possible if one or more signatories suspect a non-compliance with the deal - could eventually lead to the UN Security Council deciding whether to bring back sanctions against Iran. "My point to our American friends is, look, somehow or other you've got to stop the Iranians acquiring a nuclear weapon", Johnson said.
They are keen for it not to escalate to the stage where global sanctions are reintroduced. The second diplomat said: "Our intention is not to restore sanctions, but to resolve our differences through the very mechanism that was created in the deal".
That has accelerated sharply since 3 January, when the United States killed the most powerful Iranian military commander, Qassem Soleimani, in a drone strike in Baghdad. "Let's work together to replace the JCPOA and get the Trump deal instead", Johnson told the BBC.
After the killing of Soleimani, Iran targeted USA forces in Iraq, apparently without any casualties.
German Foreign Minister Heiko Maas said Iran's repeated violations of the deal "could not go unanswered any longer".
Tensions had been rising between the USA and Iran since May 2018, when Trump unilaterally withdrew from the landmark deal.