TEHERAN (AFP) - A top adviser to Iran's supreme leader has hinted Teheran could boost its uranium enrichment to 5 per cent for "peaceful" aims, ahead of a deadline it set for world powers to save a landmark 2015 nuclear deal.

Iran is acting on its May 8 threat to suspend from Sunday (July 7) parts of the agreement in response to US President Donald Trump's reimposition of crippling sanctions after withdrawing from the deal in May last year.

The accord capped Iran's enrichment maximum at 3.67 per cent, sufficient for power generation but far below the more than 90 per cent level required for a nuclear weapon.

Uranium enrichment "will increase as much as needed for our peaceful activities", Mr Ali Akbar Velayati, international affairs adviser to Supreme Leader Ayatollah Ali Khamenei said in an interview published on Friday (July 5) on the leader's official website.

"For Bushehr nuclear reactor we need 5 per cent enrichment and it is a completely peaceful goal," he added.

Bushehr is Iran's only nuclear power station and is currently running on imported fuel from Russia that is closely monitored by the UN's International Atomic Energy Agency.

On May 8, Iran announced it would no longer respect the limits set on the size of its stockpiles of enriched uranium and heavy water, and threatened to abandon further nuclear commitments, including exceeding the agreed uranium enrichment maximum from Sunday.

It has also threatened to resume building from that date a heavy water reactor - capable of one day producing plutonium - in Arak in central Iran, a project that had been mothballed under the deal.

The move comes in response to what Iran deems a failure by the remaining parties to the deal - Britain, China, France, Germany and Russia - to provide Teheran with relief from the US sanctions.

"The US has directly and Europeans indirectly violated" the deal, said Mr Velayati.

"We will react proportionally the more they violate it."