US State Department said the United States continues to welcome the completion of the Vienna nuclear talks with Iran.
"We remain open to continuing and ultimately to completing the JCPOA discussions in a productive manner," State Department spokesman Ned Price told reporters in Washington.
"We recognize, along with the international community, the advantage of a mechanism that ensures permanently and verifiably that Iran cannot acquire a nuclear weapon," he said.
"We've also been clear that this offer won't be on the table indefinitely."
Iran has pushed hard for relief of all sanctions but the Biden administration says it is only open to relief on measures taken over its nuclear program, not on other issues including human rights.
The sixth round of talks concluded on June 20. They are being brokered by the European Union, which like Britain, China France, Germany, and Russia remains in the deal.
Iran's incumbent President Hassan Rouhani had repeatedly promised he would get the United States to lift sanctions before the end of his term, but last week indicated this would no longer be possible and negotiations would not be complete before he leaves office.
Iran's President-elect Ebrahim Raisi will take over from Rouhani on August 5.