Iranian and U.S. negotiators have reached an agreement that calls for Iran to halt part of its nuclear program in exchange for the lifting of many of the U.S. sanctions against the Islamic regime, according to a highly placed source. Iran’s supreme leader, Ayatollah Ali Khamenei, expects a letter from President Obama in a few days guaranteeing the details of the agreement, arrived at recently during secret negotiations in Doha, Qatar. The source, who remains anonymous for security reasons and is highly placed in Iran’s regime, said that once Khamenei receives Obama’s guarantees, he will authorize an announcement by Iran...