Iran has said the US has been "procrastinating" after Tehran submitted a response to the EU's draft agreement aimed at reviving the 2015 nuclear deal.
A senior European official said this month that its draft was a final offer after 16 months of indirect talks between the US and Iran.
Last week, Tehran responded to the text with "additional views and considerations" and called on Washington to show flexibility to resolve three remaining issues.
Washington said it was studying the Iranian response but has not yet released a statement.
"The Americans are procrastinating and there is inaction from the European sides ... America and Europe need an agreement more than Iran," said Nasser Kanaani, a spokesman for the Iranian Foreign Ministry.
"Tehran wanted a sustainable deal that would preserve Tehran's legitimate rights.
"Until we agree on all issues, we cannot say that we have reached a complete agreement."
He said a prisoner swap deal with Washington was not linked to the nuclear negotiations.
The EU and US last week said they were studying Iran's response to the proposal to revive the deal, under which curbs were put on Iran's nuclear programme in return for economic sanctions relief.
"They discussed ongoing negotiations over Iran’s nuclear programme, the need to strengthen support for partners in the Middle East region, and joint efforts to deter and constrain Iran’s destabilising regional activities," the White House said.
Concerns have been raised that a failure to agree on a deal could increase the risk of conflict.
Israel has threatened military action against Iran if diplomacy fails to prevent Tehran from developing the ability to make a nuclear weapon.
Former US president Donald Trump pulled out of the nuclear deal in 2018 and reimposed sanctions. Tehran responded by breaching limits on uranium enrichment outlined in the deal.