"It is important to avoid any action that would prevent the enactment of the obligations by parties currently upholding the agreement or that might fuel an escalation," a foreign ministry spokesman said.

France, he said, "strongly calls on Iran to continue to respect all of its nuclear obligations".

French Armed Forces Minister Florence Parly has not ruled out European sanctions on Iran if it did not fulfil all of its commitments under the accord, telling broadcasters BFMTV and RMC Radio that "those are among things to be looked at".

Iran said earlier Wednesday it was responding to US sanctions imposed after President Donald Trump last year yanked his country out of the 2015 deal by deciding to stop implementing some of the restrictions imposed on it.

Specifically, it said it would stop limiting the amount of heavy water and enriched uranium it possessed.

It said it would stop adhering to other requirements of the deal unless the remaining parties to the accord -- Britain, France, Germany, Russia and China -- stepped up efforts to blunt the effect of the sanctions within 60 days.

- Ominous US military deployments -

The weakening of the nuclear accord with Iran comes amid an ominous ratcheting up of military pressure by the US, which has dispatched an aircraft carrier group and several of its huge B-52 bombers to the region close to the Islamic Republic.

The 2015 deal -- entitled the Joint Comprehensive Plan of Action -- was endorsed by the UN Security Council.

Its aim is to block pathways for Iran to acquire nuclear weapons technology and fissile material. In exchange, Iran benefitted from a lifting of international sanctions that crippled its economy.

The US sanctions imposed by Trump seek to impose even harsher curbs on Iran's economy, notably by cutting most of its oil exports and preventing it from any transactions involving the US dollar or US entities.

Washington has also designated Iran's main military force, the Islamic Revolutionary Guards Corps, which also controls swathes of the Iranian economy, as a "foreign terrorist organisation".

On Wednesday, Trump announced added sanctions on Iran's steel and mining sectors and put "other nations on notice that allowing Iranian steel and other metals into your ports will no longer be tolerated".

France, Britain and Germany early this established a special trade mechanism called Instex in a bid to allow Iran to keep trading with EU companies while bypassing the US sanctions.

Iran, though, has expressed skepticism about how effective that and other European provisions are, and US Secretary of State Mike Pompeo suggested Wednesday that Instex transactions could still be at risk of US sanctions.