DUBAI (Reuters) -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.

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.

The United States has sent its first nuclear deal proposal to Iran since negotiations began in April, a move that comes after a U.N. nuclear watchdog report indicated the Middle Eastern country significantly increased its uranium enrichment over a three-month span.