Talks to salvage the 2015 nuclear deal with Iran must take weeks rather than months, European negotiators said on Tuesday.
As the second day of talks began there appeared to be some optimism from Iran and Russia but the European delegation, in Vienna, Austria, was more downbeat.
Iran and Russia sounded upbeat early on Tuesday, with Tehran saying an accord was possible if other parties showed "good faith" and a Russian negotiator reported "indisputable progress".
"The Vienna talks are headed in a good direction ... We believe that if other parties continue the round of talks which just started with good faith, reaching a good agreement for all parties is possible," Iranian Foreign Minister Hossein Amirabdollahian said, in Iran.
France, Germany and the UK said in a statement on Tuesday that technical progress had been made in the last round and the parties now needed to fully focus on the key outstanding issues.
They said while they were not setting an artificial deadline, there were weeks not months left to strike a deal.
"We are clear that we are nearing the point where Iran's escalation of its nuclear programme will have completely hollowed out the [Joint Comprehensive Plan of Action]," they said.
"The negotiation is urgent - and our teams are here to work swiftly and in good faith towards getting a deal."
Iran's President Ebrahim Raisi is preparing to visit Russia after an invitation from Russia's President Vladimir Putin, an Iranian government spokesman said on Tuesday.
Iran's chief negotiator Ali Bagheri Kani said his delegation was fully prepared to engage and advance the talks.
After the meeting, Mr Bagheri Kani told reporters that “all sides have agreed that there is a good framework to work off of in this eighth round of talks”.
He said talks on Tuesday would include a discussion on the guarantees around lifting sanctions.
Following negotiations over general sanctions, Mr Bagheri Kani said, talks would shift to discussing financial and banking sanctions.
He said the acceptance of Iran's suggestions about the guarantees by the other parties at the plenary was a promising sign and indicated that the lifting of sanctions was seriously on the agenda.
Mr Bagheri Kani said that if an agreement is reached between all parties, the US – as the country that unilaterally withdrew from the deal – would have to first lift sanctions and Iran would reverse its enrichment based on the measures set out in the original JCPoA.
Former president Donald Trump withdrew the US from the nuclear accord in 2018 and imposed sanctions on Iran.
Russia's permanent ambassador to Vienna also expressed optimism about the latest round of talks. Mikhail Ulyanov wrote on Twitter that “the participants held businesslike and result-orientated discussions. In particular, they agreed to intensify the drafting process in order to achieve an agreement ASAP”.
All sides have indicated that diplomacy will eventually run out if no agreement is reached. Talks on the nuclear deal began between the EU, US and Iran during the Rouhani administration, but they were put on hold for a while due to Iran's election of a new president.
Enrique Mora, the EU's deputy secretary general, has said this new round of talks will be paused on Thursday and resume again after the new year on Monday morning in hopes of maintaining momentum.
On Monday morning, Iran's Mr Amirabdollahian said the new round of talks would be focused on the issue of lifting sanctions.
“The most important thing for us is to reach a point where we can verify that Iranian oil will be sold easily and without any limits, that the money for this oil will be transferred in foreign currency to Iranian bank accounts and that we will be able to benefit from all the revenue,” he said.