European allies have warned of a split with the United States over the nuclear agreement and say if Washington reimposes sanctions on Iran, the pact could fall apart.
Trump must decide by January 12 whether to extend sanctions waivers.
Trump's October decision not to certify Iran's compliance with the nuclear deal has put Washington at odds with all other signatories of the accord - Britain, France, Germany, Russia, China and the EU.
The EU's high representative for foreign affairs, Federica Mogherini, said she expected all parties to uphold the 2015 nuclear accord - a pointed message to U.S. President Donald Trump, who has severely criticized the deal.
His German counterpart Sigmar Gabriel agreed, saying the deal had "fenced in an acute crisis" and was now "a central part of our security" for Europeans.
That's right. The very complicated and important issue of a nuclear Iran, the future of the nuclear deal with the West, and the long-term security for the West and Israel, have all come down to a staring contest.
Zarif, who travelled to Moscow on Wednesday to seek Russian support, criticised what he called Washington's "destructive policy". Expect the White House to double down on non-nuclear sanctions and generate enough uncertainty to dampen investor confidence in Iran, hindering its economic recovery and further straining relations.
According to the Tehran Times, Behrooz Kamalvandi, the deputy chief of the Atomic Energy Organization of Iran, said Wednesday that Iran would ramp up uranium enrichment operations - the key process for developing nuclear bombs - to levels far higher than before the 2015 deal if the US backed out.More news: Ford is latest to be sued over Diesel Truck Emissions
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"Everyone agrees it is imperative that ALL live up to their obligations under JCPOA. IAEA has verified Iran's full compliance, but continuation will depend on full US compliance", he wrote.
"You either waive the sanctions or you don't and if you don't you're in breach of the JCPOA", the official said.
Mogherini, who played an important role in crafting the nuclear accord, has vowed to preserve the deal and has lobbied USA lawmakers in Washington.
"Europeans have so far failed to convince Iran that they can maintain the deal without the USA", he went on to say.
Iranian Foreign Minister Jawad Zarif attends a EU3-Iran meeting at EEAS headquarters in Brussels on Thursday Jan. 11, 2018.
A second diplomat said: "The date of the meeting is not a coincidence ..."
"Reports of missile transfers and Iranian assistance to countries and non-state actors in the (Middle East) region are a grave concern", the ministry said in a statement.