Armed assailants are believed to have boarded the chemical tanker Asana off the southern coast of Yemen in the Gulf of Aden on Friday and are in control of the vessel, according to maritime security sources. Based on initial assessments, the incident appeared to be related to Somali piracy rather than Yemen’s Iran-aligned Houthi militia, one of the maritime security sources said. The small tanker, which had no confirmed flag, had listed the Somali port of Bosaso as its next destination, ship...