AP — Iran says it temporarily closed parts of the Strait of Hormuz, the narrow mouth of the Persian Gulf. The move came as semiofficial Iranian news agencies reported live fire exercises in the vital waterway, through which 20% of the world’s oil passes.

The move is a rare, perhaps unprecedented shutdown of the strait, a signal from Iran of the potential fallout to the world economy if the United States goes through with threats to attack it as tensions mount between the two countries.

In past times of tension and conflict, Iran has at times harassed shipping though the narrows, and during the 1980s’ Iran-Iraq war, both sides attacked tankers and other vessels, using naval mines to completely shut down traffic at points. But Iran has not carried out repeated threats to close the waterway altogether since the 1980s, even during last year’s 12-day war when Israel and the US bombarded Iran’s key nuclear and military sites.

The extent and impact of Tuesday’s closure were not immediately known. Iranian media said it would be for several hours for “safety and maritime concerns.”

The US military’s Central Command did not immediately comment on the closure or Iran’s live fire drills. But during Iranian military exercises in the strait and nearby waters several weeks ago, it warned Tehran that any “unsafe and unprofessional behavior near US forces, regional partners or commercial vessels increases risks of collision, escalation and destabilization.”

Here’s what to know about the strait, the drill, what caused the tensions and what might happen next.

A key waterway for global shipping

The Strait of Hormuz is a bending waterway, about 33 kilometers (21 miles) wide at its narrowest point. It connects the Persian Gulf to the Gulf of Oman. From there, ships can then travel to the rest of the world. While Iran and Oman have their territorial waters in the strait, it’s viewed as an international waterway all ships can ply. The United Arab Emirates, home to the........

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