Rouhani said in televised remarks that it was a "mistake" for Europe and the United States to express concerns that the move "means we can enrich to 90 percent in one go".

"Today, we can enrich to 90 percent if we want to. But we have declared it from day one and we're keeping our word: our nuclear activities are peaceful; we are not seeking to obtain the atomic bomb."

Rouhani's comments come hours before the resumption in Vienna of talks aimed at reviving a 2015 deal that gave Iran relief from sanctions in return for curbs on its nuclear programme.

Known as the Joint Comprehensive Plan of Action, or JCPOA, the deal has been unravelling since former US president Donald Trump unilaterally withdrew from it in 2018 and imposed sanctions.

The US move has prompted Iran to retaliate by exceeding its agreed limits on nuclear activity.

Britain, France and Germany have expressed "grave concern" over the most recent enrichment move, which Iran announced on Tuesday, while also rejecting "all escalatory measures by any actor".

Iran said its decision to boost uranium enrichment to 60 percent purity was a response to an attack Sunday on Iran's Natanz nuclear facility that it blamed on arch-foe Israel.

Under the JCPOA, Iran had committed to keep enrichment to 3.67 percent, though it had stepped this up to 20 percent in January.

But Rouhani said on Thursday that Iran would swiftly return to fulfilling "all its obligations" after the Americans and Europeans resumed their own commitments.