"According to our potential agreement - WE WILL NOT ALLOW ANY ENRICHMENT OF URANIUM!" Trump writes on his platform Truth Social.
Trump's comment comes after the news site Axios published source information that Washington would still allow limited enrichment during a certain period of time.
Iran and the USA have had several rounds of talks since April, with Oman as a mediator, in an attempt to agree on a new deal for the Iranian nuclear energy program.
This is the highest level of negotiations between the countries since a previous agreement between Iran and the Western world from 2015 collapsed in 2018, during President Donald Trump's first term.
Last week, the UN's atomic energy agency) IAEA stated that Iran has accelerated its production of uranium enriched to nearly the level required to develop nuclear weapons.
But Iran denies that the country wants to develop nuclear weapons, instead claiming that the purpose of the program is purely peaceful.
American intelligence services estimate that Iran does not yet have a nuclear weapons program, but that the country has positioned itself to start one if it wanted to.