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

Even as the United States and Iran grapple with each other’s nuclear red lines, the simple fact of engagement underscores a pragmatic turn for Tehran regarding President Donald Trump.

US President Donald Trump accused Tehran on Wednesday of "slowwalking" on a nuclear deal, after Iran's supreme leader Ayatollah Ali Khamenei said the latest proposal from Washington was against the national interest.