What to know about the Strait of Hormuz as Iran plans military drill while tensions are high with US

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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.

The Strait of Hormuz resembles a bend looking down from space. Its narrowest point is just 33 kilometers (21 miles) wide. It flows from the Persian Gulf into the Gulf of Oman. From there, ships can then travel to the rest of the world. While Iran and Oman have its territorial waters in the strait, its viewed as an international waterway all ships can ply. The United Arab Emirates, home to the skyscraper-studded city of Dubai, also sits near the waterway.

The Strait of Hormuz through history has been important for trade, with ceramics, ivory, silk and textiles moving from China through the region. In the modern era of supertankers, the narrow strait proved deep and wide enough to allow for oil to pass through it. While there are pipelines in Saudi Arabia and the UAE that can avoid the passage, the U.S. Energy Information Administration says “most volumes that transit the strait have no alternative means of exiting the region.” The vast majority of the oil and gas moving through the strait goes to markets in Asia. Threats to the route have spiked global energy prices in the past, including during the 12-day war Israel launched against Iran in June.

A notice to mariners sent Thursday by radio warned that Iran planned to conduct “naval shooting” in the Strait of Hormuz on Sunday and Monday. The coordinates provided by the message put the drill potentially going into what is known as the Traffic Separation Scheme — a 3.2-kilometer- (2-mile-) wide, two-lane system in which ships coming into the Persian Gulf go north and ships exiting onto the Gulf of Oman go south. That northern lane is within the coordinates of the drill. While Iran has provided no other public details about the drills, it will likely involve the country's paramilitary Revolutionary Guard. The Guard operates a fleet of small fast-attack vessels in the strait that routinely has tense encounters with the U.S. Navy.

Early Saturday, the U.S. military's Central Command issued a strongly worded warning to Iran and the Revolutionary Guard over the drill. While acknowledging Iran's “right to operate professionally in international airspace and waters,” it warned against interfering or threatening American warships or passing commercial vessels. The command, which oversees the U.S. Navy's Bahrain-based 5th Fleet, said it “will not tolerate unsafe (Guard) actions” that could include its aircraft or vessels getting too close to American warships or pointing weapons toward them. The command added that “the U.S. military has the most highly trained and lethal force in the world.”

U.S. President Donald Trump has threatened to launch a military strike against Iran after its bloody crackdown on nationwide protests. He has laid down two red lines — the killing of peaceful protesters and Iran launching a wave of mass executions of those held. In recent days, he's also included the fate of Iran's nuclear program. The USS Abraham Lincoln aircraft carrier and supporting guided missile destroyers are now in the Arabian Sea where they could launch an attack if Trump calls for it. Iran has warned it could launch its own preemptive strike or target American interests across the Middle East and Israel. While the 12-day war saw Iran fire off ballistic missiles and Israel target its stockpile, Tehran maintains an arsenal of short- and medium-range missiles that could hit surrounding Gulf Arab states.