The U.S. State Department said early Friday that Iran’s response to a U.S. proposal via the European Union to bring back the Iran Nuclear Deal was "not constructive."
"We can confirm that we have received Iran's response through the EU. We are studying it and will respond through the EU, but unfortunately, it is not constructive."
White House National Security Council spokesperson Adrienne Watson added: "Some gaps have closed in recent weeks but others remain."
Earlier Iran’s foreign ministry said: "The text that was sent (by Iran) has a constructive approach aimed at finalizing the negotiations."
The tense exchange comes after 16 months of negotiations to revive the multinational, Obama-era deal unilaterally abandoned by then-President Donald Trump in 2018.
The EU has served as an intermediary for the indirect talks.
Under the deal, Iran curtailed its uranium enrichment in exchange for the lifting of some sanctions and was inspected by International Atomic Energy Agency surveillance through cameras and investigators.
The country could only have 300 kilograms of uranium enriched up to 3.67% under the deal but, according to the latest IAEA count, now has around 3,800 kilograms enriched up to 60% purity.
Experts warn Iran has enough 60%-enriched uranium to reprocess into fuel for at least one nuclear bomb.
Iran denies it wants to build a nuclear bomb.
Earlier this week, Iran’s foreign minister said it needed a stronger commitment from the U.S. for the revival of the deal and for the IAEA to stop its "politically-motivated" inspections.
The Associated Press and Reuters contributed to this report.