Iran will inform the United Nations nuclear watchdog agency that preparations will begin on Tuesday, Behrouz Kamalvandi, spokesman for Iran's Atomic Energy Organization, was reported saying by state media.
Earlier Monday, the director of the International Atomic Energy Agency renewed calls for Iran to provide "timely and proactive cooperation" in inspections that are part of the nuclear deal.
He said it would inform the IAEA that "Iran will announce that the process of increasing the capacity to produce UF6 (uranium hexafluoride) will start on Tuesday".
The remaining partners - Britain, China, France, Germany and Russian Federation - have scrambled to save the 2015 accord as the United States readies to reimpose sanctions on Tehran.
Iran's Supreme Leader Ayatollah Ali Khamenei had ordered the increase in a speech Monday, in which he vowed that the country would preserve its nuclear program despite the US withdrawal from the landmark 2015 accord.
The Iranian authorities have said that if the European countries fail to keep the pact alive, Tehran has several options, including enrichment of its uranium to 20% purity.
"The Atomic Energy Organization of Iran is duty-bound to prepare the ground for achieving 190 thousand SWUs", Khamenei said, insisting this production level would fall within the upper limit of what the nuclear deal (formally known as the JCPOA) allows.
"If conditions allow, maybe tomorrow night at Natanz, we can announce the opening of the center for production of new centrifuges" for uranium enrichment, Salehi said Tuesday, quoted by conservative news agency Fars.
U.S. Secretary of State Mike Pompeo later threatened Iran with the "strongest sanctions in history" if it did not comply with a list of steep demands, including ending uranium enrichment.
US President Donald Trump pulled out last month from the 2015 accord between Iran and world powers that lifted sanctions on Tehran in exchange for curbs to its nuclear program.
The Europeans have proposed hammering out a supplementary deal with Tehran covering its ballistic missile program as well as its interventions in countries such as Lebanon, Syria, Iraq and Yemen.
Speaking at a news conference with visiting Israeli Prime Minister Benjamin Netanyahu, Macron said everyone involved should "stabilize the situation and not give into this escalation, which would lead to only one thing: conflict".
Mark Dubowitz, the head of the Foundation for Defense of Democracies and a prominent critic of the agreement, said Iran's announced plans will not rescue the agreement as more companies shun the country for fear of running afoul of renewed USA sanctions.
A European source told AFP that the Iranian enrichment announcement is being interpreted as a bid to step up the pressure on Brussels to deliver on these promises.
"The people of Iran and the government of Iran will never tolerate both suffering from sanctions and nuclear restrictions", said Khamenei.