The foreign ministers of the so-called E3, along with the EU’s foreign policy chief, held their first call with Iran’s foreign minister Abbas Araqchi since Israel and the US carried out air strikes in mid-June on Iran’s nuclear programme.

Speaking after the call, a French diplomatic source said the ministers had called on Iran to resume diplomatic efforts immediately to reach a “verifiable and lasting” nuclear deal.

The three countries, along with China and Russia, are the remaining parties to a 2015 deal with Iran that lifted sanctions on the country in return for restrictions on its nuclear programme.

A UN Security Council resolution which enshrines the deal expires on Oct 18 and under its terms, UN sanctions can be reimposed beforehand. The process would take about 30 days.

The Europeans have repeatedly warned that unless there is a new nuclear accord they will launch the “snapback mechanism”, which would restore all previous UN sanctions on Iran if it is found to be in violation of the agreement’s terms.

“The ministers also reiterated their determination to use the so-called ‘snapback’ mechanism in the absence of concrete progress toward such an agreement by the end of the summer,” the diplomatic source said.

The source did not elaborate on what concrete progress would entail.

Since the air strikes, inspectors from the UN atomic watchdog have left Iran. While Iran has suggested it is open to diplomacy, there are no indications a sixth round of nuclear talks between Washington and Tehran will resume imminently.

Diplomats say that even if they were to resume talks, reaching a comprehensive accord before the end of August – the final deadline the Europeans have given – seems unrealistic, especially without inspectors on the ground to assess Iran’s remaining nuclear programme.

Two European diplomats said they hoped to coordinate strategy with the US in the coming days with a view to possibly holding talks with Iran soon.