DUBAI, United Arab Emirates (AP) — The Strait of Hormuz, the narrow mouth of the Persian Gulf, again has become a focus of tensions as Iran prepares to launch a military drill that could see fire into a lane crucial for global shipping. Iran has warned ships that it will conduct a live fire drill Sunday and Monday in the strait, which sees a fifth of all oil traded pass through the tight corridor between the Islamic Republic and Oman. The U.S. military's Central Command issued its own warning early Saturday, telling Tehran that any “unsafe and unprofessional behavior near U.S. forces, regional partners or commercial vessels increases risks of collision, escalation and destabilization.” Here's what to know about the drill, the U.S. warning, what caused the tensions and what might happen next in the Strait of Hormuz.