Iran on Monday demanded assurances from Washington that U.S. sanctions would be lifted as part of any nuclear deal, following reports that the White House had submitted a proposal it considers "acceptable."

With Iran and the United States engaged in talks over Tehran's nuclear program since April, Washington's proposal for a deal came after a leaked U.N. report said Iran had stepped up production of highly enriched uranium.

Iran's top diplomat and lead nuclear negotiator, Abbas Araghchi, was due to meet the head of the U.N.'s International Atomic Energy Agency (IAEA) in Cairo on Monday, a day after the report was leaked.

Tehran has rejected the report, warning it would retaliate if European powers that have threatened to reimpose nuclear sanctions "exploit" the report.

The United States and Western countries have accused Iran of seeking nuclear weapons, a charge Tehran has repeatedly denied, insisting it needs uranium for civilian power production.

Araghchi said Saturday that he had received "elements" of a U.S. proposal for a nuclear deal following five rounds of talks mediated by Oman.

On Monday, Foreign Ministry spokesperson Esmaeil Baqaei told a news conference in Tehran: "We want to guarantee that the sanctions are effectively lifted."

"So far, the American side has not wanted to clarify this issue," he added.

He also condemned the report and threatened an Iranian response.

The report, Baqaei said, was the result of "pressure exerted by certain European countries on the agency."

"If they want to further exploit this political report ... they will surely have to face a proportionate response from Iran," he added.

'Red line'

The remarks come after a report by the U.N. agency showed Iran has stepped up production of uranium enriched up to 60% – close to the roughly 90% level needed for atomic weapons.

The U.S. envoy in the nuclear talks said last month that the administration of President Donald Trump would oppose any enrichment.

"An enrichment programme can never exist in the state of Iran ever again. That's our red line. No enrichment," Steve Witkoff told Breitbart News.

Iran has vowed to keep enriching uranium "with or without a deal" on its nuclear program.

The United States has sent Iran a proposal for a nuclear deal that the White House called "acceptable" and in its "best interest" to accept, U.S. media reported on Saturday.

The New York Times, citing officials familiar with the diplomatic exchanges, said the proposal calls on Iran to stop all enrichment and suggests creating a regional grouping to produce nuclear power.

Iran has held five rounds of talks with the United States in search of a new agreement to replace the deal with major powers that Trump abandoned during his first term in 2018.