Iran is poised to reject a U.S. proposal to end a decades-old nuclear dispute, an Iranian diplomat said on Monday, dismissing it as a "non-starter" that fails to address Tehran's interests or soften Washington's stance on uranium enrichment.

White House press secretary Karoline Leavitt revealed that a "detailed and acceptable" proposal was sent to Iran by Steve Witkoff.

The preliminary U.S. proposal came as a confidential U.N. report described an Iranian initiative that had multiplied Tehran’s stockpile of near-bomb-grade uranium.