Iran’s supreme leader has denounced a proposal by the United States aimed at curbing Tehran’s nuclear efforts and demanded that his country retains national independence amid reports of Washington offering to become involved in Tehran’s nuclear program.

Iran’s supreme leader, Ayatollah Ali Khamenei, said on Wednesday that abandoning uranium enrichment was “100 percent” against Tehran’s interests, effectively rejecting a key U.S. demand in weeks of tense negotiations over Iran’s nuclear program.

Iran rejected a U.S.-proposed nuclear deal Wednesday, vowing to continue enriching uranium while negotiations appear to be stalling after five