OSAKA (AFP) - There is "no rush" to resolve tensions between the United States and Iran that have raised fears of a military conflict, US President Donald Trump said on Friday (June 28).

"We have a lot of time. There's no rush, they can take their time. There is absolutely no time pressure," he said in Osaka, where world leaders are meeting for the G-20 summit.

"Hopefully in the end it's going to work out. If it does, great, if it doesn't, you'll be hearing about it."

It was a more conciliatory tone than the bellicose rhetoric issued by the US leader just before his trip to Japan, where tensions with Iran will be among the top items on the agenda.

On Wednesday, the US president said any conflict "wouldn't last very long", an assertion quickly rejected by Iran's foreign minister, as well as French President Emmanuel Macron.

"'Short war' with Iran is an illusion," Foreign Minister Javid Zarif wrote on Twitter.

Tensions between Teheran and Washington have spiralled since Mr Trump withdrew from an international nuclear deal.

Iran has been gradually stepping back from its commitments under the deal, and had been expected to surpass agreed limits on enriched uranium reserves on Thursday.

But a diplomatic source in Vienna said Teehran would not after all exceed the limit, suggesting there could be a "political reason" for this.

But an Iranian official said the limit had not been breached because of "technical" reasons.