The indirect negotiations in Doha began on Tuesday and are an attempt to reboot long-running European Union-mediated talks in Vienna on restoring the landmark nuclear agreement between Tehran and world powers.

"Two intense days of proximity talks in Doha," Enrique Mora, the European Union's coordinator for the talks, said on Twitter.

"Unfortunately, not yet the progress the EU team as coordinator had hoped-for. We will keep working with even greater urgency to bring back on track a key deal for non-proliferation and regional stability."

The deal, which gave Iran sanctions relief in return for Tehran curbing its nuclear programme, was abandoned unilaterally by former US president Donald Trump in 2018.

Talks on reviving the deal had been taking place since April 2021 in Vienna, before the process stalled last March.