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

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.

A classified International Atomic Energy Agency report found Iran, since February, produced 300 pounds of uranium enriched to 60%, a step away from weapons-grade.