Iran has said it will breach an internationally agreed limit on its stock of low-enriched uranium in 10 days.
"We have quadrupled the rate of enrichment (of uranium) and even increased it more recently, so that in 10 days it will bypass the 300 kg limit," Behrouz Kamalvandi, a spokesman for Iran's Atomic Energy Organization spokesman, said on state TV.
"Iran's reserves are every day increasing at a more rapid rate," he added.
The comments drew concern in the West where nations were striving to save a landmark nuclear deal.
They were likely to worsen already-strained tensions between Tehran and Washington.
Germany urged Tehran to meet all its obligations under the 2015 accord, while Britain said if Iran breached limits agreed under the deal then, London would look at "all options".
Israel, a close ally of the US and Iran's arch-foe, urged world powers to step up sanctions against Tehran swiftly should it exceed the enriched uranium limit.
The US government has claimed that Iran was responsible for the attack on two oil tankers near the Gulf of Oman on Thursday.
Iran categorically rejected claims, denying it had any role and saying it was responsible for maintaining the security of the Strait of Hormuz where the incidents took place.
Iran’s Supreme Leader Ayatollah Ali Khamenei said on the same day as the attacks that "even if Iran wanted to build an atomic bomb, America could not do anything" to stop it, adding that it was not his country's wish to do so.
He made the comments on Thursday during a meeting in Tehran with Japanese Prime Minister Shinzo Abe, who was acting as an interlocutor for US President Donald Trump to ease tensions between Washington and Iran.
In May, Tehran said it would reduce compliance with the nuclear pact in protest at the US decision to unilaterally pull out of the agreement and reimpose sanctions last year.
Iran should curb its uranium enrichment capacity under the deal's terms, limiting its stock of low-enriched uranium to 300 kilograms of uranium hexafluoride enriched to 3.67%, or equivalent, for 15 years.
UN inspections under the deal confirmed that Iran has been meeting its commitments.
President Hassan Rouhani said the deal's collapse would not be in the interests of the region or the world, urging European signatories to speed up their efforts to salvage it.