Last week, the Islamic republic returned to international talks in Vienna aimed at reviving the 2015 nuclear deal after a five-month pause.

On Wednesday it submitted two draft resolutions on the lifting of US sanctions and nuclear-related measures.

But at the weekend the United States, as well as European participants at the Vienna talks, accused Iran of back-tracking.

A senior US administration official said the proposals "walked back any of the compromises that Iran had floated" during the previous six rounds of negotiations.

The official accused Iran of seeking to "pocket all of the compromises that others -- the US in particular -- had made and then ask for more".

On Monday, Iranian foreign ministry spokesman Saeed Khatibzadeh hit back.

"Our texts are fully negotiable," he told a news conference about the draft proposals," also charging that the other parties "want to play a blame game".

"We are waiting naturally to hear the other side's opinion concerning these texts and whether they have a real (counter) offer to make to us in writing," Khatibzadeh added.

The seventh round of nuclear talks ended Friday after five days in Vienna, with delegations returning to their national capitals and expected to go back to Austria next week.

Khatibzadeh said the negotiations were expected to resume "at the end of the week", without elaborating.

The landmark 2015 nuclear accord was initially agreed between Iran and Britain, China, France, Germany, Russia and the United States.

The deal is aimed at putting curbs on Iran's nuclear programme to ensure it could not develop an atomic weapon, in exchange for sanctions relief for Tehran.

But it began unravelling in 2018 when then US president Donald Trump pulled out and reimposed sanctions, prompting Iran to start exceeding limits on its nuclear programme the following year.

Iran has always insisted that its nuclear programme is peaceful.