Talks about reviving the 2015 Iran nuclear deal are moving forward in Vienna slowly but with some growth, the US has said.
On Tuesday, US State Department spokesman Ned Price said negotiations had shown "modest progress" and delegates were hoping to build on that in the coming week.
The eighth round of the talks, which started after Iran's hardline president Ebrahim Raisi took office, has been focused on lifting crippling sanctions imposed by the Trump administration.
Former president Donald Trump pulled the US out of the 2015 accord, known as the Joint Comprehensive Plan of Action and reinstated sanctions on Iran's economy.
A year after Mr Trump's decision, Iran abandoned the terms of the agreement, enriching uranium well above the agreed limits and increasing its installation of advanced centrifuges.
Iran has maintained that its goal at the talks is sanctions relief, while the US has been rigid in its stance against lifting them until Tehran curtails its nuclear programme.
Iran's chief negotiator Ali Bagheri on Tuesday held a meeting with the EU's Enrique Mora and the chief negotiators from China and Russia and also the heads of the EU, Germany, UK and France delegations.
China and Russia have taken centre stage since the nuclear talks restarted, working to co-ordinate liaisons between all the original signatories. On Monday, Iran's foreign ministry spokesman struck a positive tone when discussing the talks at his press briefing, saying his country had detected a new "realism" from the West.
Sanctions relief 'at the heart' of negotiations
Meanwhile, Mr Price outlined Washington's stance at his briefing on Tuesday, saying “sanctions relief and the steps that the United States would take when it comes to sanctions – together with the nuclear steps that Iran would need to take if we were to achieve a mutual return to compliance with the JCPOA – that’s really at the heart of the negotiations that are ongoing in Vienna right now."
Despite the slow progress, the arrival of South Korea's Vice Foreign Minister Choi Jong-kun on Tuesday was being taken by some as a positive sign for the ongoing talks. South Korea has been holding nearly $7 billion of Iran's assets frozen due to sanctions.
Washington has yet to approve a release of the funds.
Over the course of the past few years, Iran has repeatedly demanded that its funds be released.
Before the start of talks with the Biden administration, analysts had suggested that the release of Iran's frozen assets could be a good-faith move by the US administration.
While no major breakthroughs have been announced so far negotiators have said they hope to have talks wrapped up by the end of January or early February.
