Abbas Araghchi will remain part of Iran's negotiating team in talks on reviving a landmark nuclear agreement with major powers but will no longer be styled chief negotiator.

He will be replaced as deputy minister by Ali Bagheri, a protege of ultraconservative President Ebrahim Raisi who served as his deputy for international affairs when Raisi was judiciary chief.

Raisi became president in early August, taking over from moderate Hassan Rouhani, the principal architect on the Iranian side of the 2015 nuclear agreement.

The deal gave Iran an easing of Western and UN sanctions in return for tight controls on its nuclear programme, monitored by the UN.

But in 2018 then US president Donald Trump dealt it a crippling blow by pulling out and reimposing swingeing US sanctions.

Trump's successor President Joe Biden has said he wants to bring Washington back into the agreement but talks on doing so have stalled since the change of president in Tehran.

Bagheri has repeatedly criticised former president Rouhani for the strict limits he agreed to on Iran's nuclear activities and his willingness to grant "foreigners" access to Iranian nuclear plants and other "sensitive security facilities".