Yemen’s powerful Shiite Houthi rebels shelled the residence of the country’s embattled president Tuesday and simultaneously swept into the presidential palace in the capital, Sanaa, as a top military commander warned that a full-fledged “coup” was underway. President Abed Rabbo Mansour Hadi was inside the residence as it came under “heavy shelling” for half an hour but he was unharmed and protected by guards, officials said. In New York, the U.N. Security Council held an emergency meeting over the chaos in Sanaa. The shelling was a dramatic development that put the U.S.-backed Hadi into a precarious position and represented the...