"They won't exceed it today," the source told AFP, speaking on condition of anonymity.

The source suggested there might be a "political reason" for this, given the intensified efforts by European governments in recent days to de-escalate tensions in the Gulf region.

There was no indication to suggest the agreed limit would be exceeded this weekend either, the source added, underlining that Tehran can suspend its uranium enrichment activities at any time.

Iran said 10 days ago that it would surpass the agreed 300-kilogramme (660-pound) reserve of enriched uranium on June 27 because it no longer felt bound by the 2015 deal which the United States unilaterally pulled out of in May 2018.

Vienna is home to the UN's nuclear watchdog, the International Atomic Energy Agency or IAEA, which is responsible for monitoring whether Iran is sticking to the terms of the nuclear deal.

Tehran has also threatened to start enriching uranium above the agreed purification level of 3.67 percent starting from July 7.

Under the landmark deal signed with world powers in 2015, Iran pledged to reduce its nuclear capacities for several years and to allow IAEA inspectors into the country to monitor its activities in return for relief from international sanctions.

The deal set a limit on the number of uranium-enriching centrifuges, and restricted Iran's right to enrich uranium to no higher than 3.67 percent, well below weapons-grade levels of about 90 percent.

But the deal has come under severe strain since Washington pulled out of it last year and slapped new economic sanctions on the Islamic republic.

On Tuesday, in a gesture seemingly aimed at reining in soaring tensions with the US, Iranian President Hassan Rouhani told French President Emmanuel Macron in a telephone call that Iran "never seeks war" with any country.

Macron, for his part, said on the sidelines of a G20 meeting in Tokyo that he would do "the maximum" to "avert military escalation" between Iran and the US.

US President Donald Trump said Wednesday he does not want a war with Iran, but warned that if fighting does break out, it "wouldn't last very long".

Macron reiterated that France shared the US "strategic objective" that Iran should not be allowed to develop a nuclear weapon.