The US and Europe strongly agree on the importance of reviving talks with Iran for a deal to limit Tehran's nuclear ambitions, US Secretary of State Antony Blinken said on Sunday.
Washington was “absolutely in lockstep” with Britain, Germany and France on getting Iran back into a nuclear deal, Mr Blinken said.
But he added that it was unclear if Iran was willing to rejoin the talks in a “meaningful way".
Last week, Iran's nuclear talks envoy Ali Bagheri Kani said he believed talks could resume by the end of November, but gave no date.
Europe has strongly urged Iran to restart talks on a new nuclear accord.
These were being held in Vienna, but were paused in June because of a government transition in Iran, after the conservative President Ebrahim Raisi was elected to office.
Under a previous agreement between 2015 and 2018, Iran curtailed nuclear work seen as creating a risk of nuclear weapons being developed, in exchange for a lifting of global sanctions.
In 2018, then-president Donald Trump withdrew the US from the deal, prompting Tehran to breach limits on uranium enrichment set by the pact.
Iran seemed to confirm Mr Blinken's doubts regarding the possibility of new talks, following his interview with CNN on Sunday.
“It is enough for [US President Joe] Biden to issue an executive order tomorrow and they [the US] announce they are rejoining the pact from the point where his predecessor left the deal,” Iranian Foreign Minister Hossein Amirabdollahian said on Sunday.
Hardliners in Tehran have called for Washington to move first on any nuclear deal, demanding that sanctions are lifted before dialogue can resume.
“If there is a serious will in Washington to return to the deal, there is no need for all these negotiations at all,” Mr Amirabdollahian said.
Last week, Rafael Grossi, head of UN atomic watchdog the International Atomic Energy Agency, said that he had not been given access to Mr Amirabdollahian to continue discussions.
“I need to have this contact at the political level. This is indispensable. Without it, we cannot understand each other,” Mr Grossi said.
He added that Iran could be months away from having enough material to create a nuclear weapon, and that monitoring needed to recommence to rebuild trust.