"Cooperation with the International Atomic Energy Agency (IAEA) within the framework of safeguards regulations should be maintained," Ayatollah Ali Khamenei said during a meeting with Iranian nuclear scientists, experts and officials.

In his Sunday speech, the supreme leader said agreements could be reached in certain fields, but stressed that "the existing infrastructure of the nuclear industry should not be touched".

Iran's Atomic Energy Organisation "need not succumb to the pressure of unfounded claims and demands based on bullying", Khamenei said, without specifying the demands or claims.

Iran's nuclear programme has long been the subject of scrutiny from Western powers, resulting in sanctions that have crippled the country's economy.

A 2015 nuclear accord between Iran and world powers gave the Islamic republic relief from international sanctions in return for curbs on its atomic programme.

But in 2018 the United States unilaterally withdrew from the deal and reimposed sanctions, prompting Tehran to walk back its own commitments to restrict nuclear activity including uranium enrichment.

Efforts to revive the deal have so far failed to yield results.

In late May, after months of wrangling over the question of traces of nuclear material found in previously undeclared sites, the UN agency announced progress and declared the file closed.

However, the watchdog also noted that Iran has significantly increased its stockpile of enriched uranium in recent months.

Iran has always denied any ambition to develop nuclear weapons capability, insisting that its activities are entirely peaceful.

Khamenei on Sunday reiterated the denial of moves towards acquiring a nuclear weapon, in keeping with "our Islamic principles".

"Otherwise they would not have been able to stop it," he continued, "just as they have not been able to stop our nuclear progress until now."