Diplomats say time is running low to resurrect the pact, which then-US President Donald Trump abandoned in 2018, angering Iran and dismaying the other world powers involved — Britain, China, France, Germany and Russia.
Six rounds of indirect talks were held between April and June. The new round begins after a hiatus triggered by the election of a new Iranian president, Ebrahim Raisi, a hardline cleric.
Tehran’s new negotiating team has set out demands that US and European diplomats consider unrealistic. They are insisting that all US and EU sanctions imposed since 2017, including those unrelated to its nuclear programme, be dropped.
In parallel, Tehran’s conflicts with the UN atomic watchdog, which monitors the nuclear programme, have festered.
Iran has pressed ahead with its uranium enrichment programme and the IAEA says its inspectors have been treated roughly.