Iran is preparing a counter-proposal after rejecting the U.S. nuclear deal, prompting President Trump to caution that "time is running out."

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’s supreme leader has criticized an initial proposal from the United States in negotiations over Tehran’s rapidly advancing nuclear program.