The Trump administration is barring Iran’s top diplomat from entering the United States this week to address the United Nations Security Council about the U.S. assassination of Iran’s top military official in Baghdad, violating the terms of a 1947 headquarters agreement requiring Washington to permit foreign officials into the country to conduct U.N. business, according to three diplomatic sources. Iranian Foreign Minister Mohammad Javad Zarif requested a visa a “few weeks ago” to enter the United States to attend a Jan. 9 Security Council meeting on the importance of upholding the U.N. Charter, according to a diplomatic source familiar with...