Iran's Supreme Leader Ali Khamenei sent a letter to Russian President Vladimir Putin to brief him on nuclear negotiations with the U.S. as tensions between the two countries continue to rise. The Trump administration has threatened to bomb Iran and extend tariffs if an agreement is not reached. Iran's foreign minister delivered the letter to Moscow, addressing regional and bilateral issues. Russia, a long-time ally of Iran, plays a role in the nuclear negotiations as a veto-wielding U.N. Security Council member and a signatory to a previous nuclear deal.