US Secretary of State Antony Blinken said on Sunday that the United States was "absolutely in lock step" with European allies on getting Iran back into the 2015 nuclear deal.
But the top US diplomat added it was unclear if Tehran was willing to rejoin the talks in a "meaningful way."
Iran stopped participation in multilateral talks in Vienna in June, refusing to announce an exact date for their its return.
Blinken's remarks in an interview with CNN on Sunday come a day after the United States, Germany, France and Britain urged Iran to resume compliance with a 2015 nuclear deal in order to "avoid a dangerous escalation."
The accord, under which Iran curtailed nuclear work seen as a risk of developing nuclear weapons in exchange for a lifting of global sanctions, unraveled in 2018 after then-President Donald Trump withdrew the United States, prompting Tehran to breach limits on uranium enrichment set by the pact.
"It really depends on whether Iran is serious about doing that," Blinken said about Iran rejoining the nuclear talks. "All of our countries, working by the way with Russia and China, believe strongly that that would be the best path forward", he added.
Leaders of the four countries hoping to persuade Tehran to stop enriching uranium to near-weapons-grade levels, said on Saturday they wanted a negotiated solution. Iran is enriching uranium to 20 and 60 percent purity, which has no civilian use. The process reduces the time Tehran would need to develop a nuclear device.
"But we do not yet know whether Iran is willing to come back to engage in a meaningful way," Blinken said on Sunday. "But if it isn't, if it won't, then we are looking together at all of the options necessary to deal with this problem."
Iran's foreign minister said separately on Sunday that if the United States was serious about rejoining Tehran's 2015 nuclear deal with world powers, President Joe Biden could just issue an "executive order," the state-owned Iran newspaper reported.
"It is enough for Biden to issue an executive order tomorrow and they (U.S.) announce they are rejoining the pact from the point where his predecessor left the deal," Iranian Foreign Minister Hossein Amirabdollahian said. "If there is a serious will in Washington to return to the deal, there is no need for all these negotiations at all."
But this fails to take into consideration the different current circumstances including the complexity of the sanctions and the reversal of gains Iran has made in its nuclear program since 2018.
Talks between Iran and world powers aimed at salvaging the deal, which started in April, are slated to resume at the end of November, the Islamic Republic's top nuclear negotiator said on Wednesday.
With reporting by Reuters