France said on Friday that negotiators had made progress towards restoring the Iran nuclear deal, but that time was running short to reach an agreement.

Foreign Minister Jean-Yves Le Drian said the talks in Vienna were heading in a positive direction and that he was "convinced we can reach a deal".

But although "bits of progress have been made in the last few days", time is of the essence because "if we don't get an accord quickly there will be nothing to negotiate", he told French broadcasters.

His language echoed that of Britain, which said in talks with Israel this week that time was running out for a deal. Germany said on Wednesday that the negotiations were "entering a crucial phase" and that there was "not much time".

Washington said on Tuesday that the reason for the ticking clock was that Iran's "accelerating nuclear steps" would "increasingly diminish the non-proliferation benefits" of the deal if no agreement is reached.

Iran displayed three ballistic missiles in central Tehran on Friday – known as Dezful, Qiam and Zolfaghar – which the Islamic Revolutionary Guard Corps said had ranges up to 1,000 kilometres.

The eighth round of talks resumed on Monday, the latest step in negotiations aimed at restoring the 2015 deal between Iran, the US, Britain, France, Germany, Russia and China.

The accord lifted sanctions on Iran in exchange for restrictions on its nuclear activities. The US pulled out under former president Donald Trump in 2018 and restored punitive measures against Tehran, which responded by breaching many of the limits it had agreed to in Vienna.

Iran refuses to meet directly with US officials to discuss a restoration of the deal, meaning that diplomats from the other parties must shuttle between the two sides.

This week's talks featured the arrival of South Korea's vice foreign minister to discuss the possible release of $7 billion in frozen Iranian assets held in Korea because of US sanctions. Any such release would need to be approved by Washington.

Seoul said the vice minister had agreed with the Iranians that the release of the frozen assets "should take place in an urgent manner".