"Iran, I think, knows what it needs to do to come back into compliance on the nuclear side. And what we haven't seen is whether Iran is ready and willing to make a decision to do what it has to do. That's the test and we don't yet have an answer." he told ABC's George Stephanopoulos in an interview to be aired on Sunday night.
The US is "committed to trying to see if Iran will come back into compliance with the nuclear agreement," he added, saying they can then look at other issues, including Iran's support for foreign proxies.
The nuclear deal, also known by its full name, the Joint Comprehensive Plan of Action (JCPOA), was signed in 2015, but broke apart in 2018 after former US President Donald Trump withdrew Washington from the deal, reimposing harsh sanctions on Iran.
Since then, Tehran has repeatedly violated its obligations as part of the deal.
Talks are continuing in Vienna to try and salvage the agreement, with the US taking part in indirect discussions with Iran.
The US previously struck a positive tone about the talks.
“Returning to the deal, as you know, would require Iran to significantly roll back its nuclear program and block every available pathway to a nuclear weapon,” White House Press Secretary Jen Psaki told reporters during a press briefing earlier this month. “But the talks are continuing; that is a good sign."
Iran has previously said it would return to the deal, but only if the US fully lifted sanctions first.
