DUBAI, United Arab Emirates—A remotely piloted boat packed with explosives targeted the Saudi port of Yanbu in the Red Sea on Tuesday, the kingdom said, with the blast sending black smoke into the sky off the coast. Saudi Arabia claimed to have intercepted and destroyed the attack boat. However, private security firms suggested commercial traffic near the port may have been hit in the assault. Details remained scarce, but the incident comes after a series of attacks on shipping in the wider Mideast region amid a shadow war between Iran and Israel and against the backdrop of ongoing negotiations between Tehran and world powers over Iran’s tattered nuclear deal. The incident also comes amid the kingdom’s years-long war against Yemen’s Houthi rebels. The Houthis have in the past used bomb-laden drones and explosive-packed boats in attacks targeting the kingdom. However, the rebels did not immediately claim any assaults on Tuesday …