Iran has demoted its chief nuclear negotiator, replacing him as deputy foreign minister with an opponent of concessions to the West, state media reported Wednesday.

Analysts said the reshuffle was intended as a warning that a much tougher policy could lie ahead if talks drag on over bringing Washington back into a landmark nuclear deal that was abandoned by former US president Donald Trump.

Abbas Araghchi was one of the key negotiators of the 2015 agreement but his role in the talks will now be limited to that of ministry adviser, state media said.

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 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 president 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, 53, has repeatedly criticised 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".

Analyst Mehdi Zakerian said the appointment put Iran's nuclear policy firmly in the hands of ultraconservatives close to Raisi.

"In the Raisi administration, the key personalities at the the negotiating table are now Iranian Atomic Energy Organisation chief Mohammad Eslami and Ali Bagheri," Zakerian told AFP.

"Bagheri's appointment should be seen as a clear warning to the West as it's likely the new team will throw into question the whole basis of the nuclear deal and abandon all of Iran's commitments if the Americans delay their return to the 2015 agreement."

After Raisi became president in August, Iran suggested that indirect negotiations with Washington on its return to the deal were unlikely to resume for two to three months.

US Secretary of State Antony Blinken warned last week that time was running out for a deal that must also tackle Iran's retaliatory suspension of many of its own commitments.