Washington wants its European allies to agree on further measures against Iran in return for keeping a landmark nuclear deal with Tehran alive, US officials said Friday.
Speaking after closed-doors meetings between the US, Iran, Russia and other major world powers in Vienna, US diplomats indicated that an American walkout from the deal isn't a foregone conclusion yet, despite harsh words about the agreement from US President Donald Trump.
"In order for the United States to remain in the deal, the United States and Europe must come to an agreement to address sunsets, inspections, and long range ballistic missiles," said Brian Hook, the State Department official who led the US delegation.
Washington opposes the expiry over time of restrictions on Iran's nuclear enrichment program — stipulated in one of the deal's sunset clauses — and wants the UN to get greater powers to inspect Iran's military sites, too.
Although the issues are currently outside the nuclear agreement, the US also wants European countries to support a clampdown on Iran's ballistic missile program and the country's activity beyond its borders, such as by designating the political wing of Lebanon's Hezbollah a terrorist organisation.
"The president has instructed us to see if we can come to an agreement with the Europeans by May 12," said Mr Hook.
He confirmed that American diplomats also met with an Iranian delegation on the sidelines of a gathering of the so-called Joint Comprehensive Plan of Action Joint Commission, or JCPOA, but didn't provide details.
Such discussions between the US and Iran have occurred occasionally on the margins of regularly scheduled Iran deal talks.
A senior State Department official in Washington said the US side has used the opportunity to raise the cases of Americans imprisoned or missing in Iran.
The periodic meeting of the JCPOA was being closely watched for an indication of American thinking following Mr Trump's firing of Secretary of State Rex Tillerson.
Mr Trump has vowed to walk away from the 2015 agreement in mid-May unless European countries join the US in addressing what the president says are its key flaws. These include no penalties for Iran's missile work and support for militant groups in Lebanon, Syria, Yemen and elsewhere.
Mr Tillerson's firing and the choice of anti-Iran hard-liner Mike Pompeo to replace him have fuelled speculation that Washington will pull out - a move that likely would kill the deal.
Iranian Deputy Foreign Minister Abbas Aragchi and other delegates refused to comment on the closed-door session after it wrapped up.
But Mr Aragchi told a parliamentary committee in Tehran on Wednesday that Mr Tillerson's ouster was proof that Mr Trump would pull out and promised that Iran would withdraw if the US does.
Mr Hook said the meetings in Vienna had been productive, insisting that "the US is meeting its commitments under the Iran nuclear deal and we are holding Iran accountable for its commitments".
"We believe that we can work within the Iran nuclear deal to strictly enforce it while we are working on all of the aspects outside of Iran's nuclear program," he said.
The nuclear deal, which was negotiated during the Obama administration, limits Iran's enrichment and stockpiling of material that could be applied to a nuclear weapons program. In exchange, Tehran was granted widespread relief from international trade, oil and banking sanctions.
Mr Trump's next deadline to extend some of those concessions is May 12.
EU foreign ministers, who will discuss the issue Monday in Brussels, are expected to affirm that they believe the deal with Iran is good, and work to discourage Mr Trump from pulling out of the deal. At the same time, they're expected to start putting greater stress on Iran's missile development and its destabilising role in the region.