"We are still working through a number of difficult issues. As I said before, the onus is on Tehran to make difficult decisions," said State Department spokesman Ned Price.
"But we have negotiated for the better part of a year of course indirectly through our allies and partners in good faith in a constructive manner to get us to this point. We are still at a point where if those decisions are made, we could reach a mutual return to compliance very soon," he added.
Price said an agreement is neither imminent, nor is it certain.
"And so, that is precisely why for the better part of the year, we have been preparing for either contingency, for either scenario, a world in which we have a mutual return to compliance," he added.
Indirect negotiations between the US and Iran have been ongoing since April 2021. They have been facilitated by the other participants of the Joint Comprehensive Plan of Action (JCPOA) in protracted shuttle diplomacy.
The agreement placed unprecedented curbs on Iran's nuclear program and subjected Tehran to an international inspections regime verified by the International Atomic Energy Agency (IAEA).
Former US President Donald Trump unilaterally withdrew from the JCPOA in 2018, in a futile effort to bring Iran back to negotiations for what his administration maintained would be a more wide-ranging agreement.
Trump re-imposed US sanctions lifted under the 2015 pact and imposed new economic penalties.
Rather than pursue negotiations, Tehran chose to take steps away from its nuclear-related commitments in retaliation for Trump's actions.