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

President Trump accused Iran of "slow-walking their decision" in nuclear negotiations on Wednesday hours after Iranian Supreme Leader Ali Khamenei criticized the U.S. proposal for a deal. Why it matters: Khamenei's speech foreshadowed the official Iranian response to the U.S. proposal, which American officials expect will be negative.