Saudi Arabia called the incidents “a serious threat to the security and safety of maritime traffic” but did not single out any alleged perpetrator. Iran’s Foreign Ministry said it was still seeking clarification and cautioned against a possible “conspiracy orchestrated by ill-wishers.”

Only last week, the U.S. Maritime Administration warned of Iranian interference in the region. “Since early May, there is an increased possibility that Iran and/or its regional proxies could take action against U.S. and partner interests. . . . Iran or its proxies could respond by targeting commercial vessels, including oil tankers, or U.S. military vessels in the Red Sea, Bab el-Mandeb Strait or the Persian Gulf.”

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As of Monday, there was no evidence of Iranian links to the attacks alleged by Saudi Arabia against commercial vessels.

The incidents come not only amid heightened tensions between Iran and its foes in the region, but also between Tehran and Washington. One week ago, the U.S. government deployed the USS Abraham Lincoln carrier strike group and a bomber task force to the U.S. Central Command (Centcom) region.

It was not clear if the deployment at the time was connected to more recently voiced concerns over possible Iran-linked attacks on commercial vessels. But the deployment of additional U.S. resources to the region amid heightening tensions has become a more regular occurrence: The reason is the narrow stretch of water at the mouth of the Persian Gulf, the Strait of Hormuz, which any ship has to transit to get from the Gulf of Oman into the Persian Gulf, or back.

Amid threats from abroad, Iran has often been quick to remind the world of its key location along one of the world’s main oil tanker routes. It once again threatened to close that key transport route in recent weeks. When Bahrain, a Persian Gulf nation with a sizable U.S. troop presence, warned that it would not allow Iran to proceed with such a move, an Iranian official responded: “Mind your small size and do not threaten someone bigger than yourself.”

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Why is the Strait of Hormuz so crucial?

The Strait of Hormuz is one of the world’s most crucial transport routes for oil. About a third of the world’s oil tanker traffic passes through the strait, which is bordered by Iran and Oman. In 2016, 18.5 million barrels of petroleum were shipped through it every day, making it the world’s single most important maritime route for many nations’ oil supplies.

Theoretically, Iran could attempt to cut off the Strait of Hormuz by deploying its naval vessels or laying mines, which could take months to clear. At its narrowest point, the strait’s shipping route is only two miles wide. But the U.S. military has extensive footholds in the region, including the headquarters for the Navy’s 5th Fleet in Bahrain.

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What would be the impact if Iran blocked the Strait of Hormuz?

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If that route were inaccessible, the world’s supply in shipped daily global oil exports would suddenly drop by about 30 percent, experts predict. Overall oil supplies would drop by about 20 percent, according to numbers compiled before the recent U.S. sanctions on Iranian oil exports took effect.

Some of the oil may be rerouted via pipelines that have been expanded over fears of an Iranian-Western clash, but those are still limited in capacity and more expensive.

As a result, oil prices would immediately spike, as Arab oil suppliers would lose their market access either entirely or to a large extent. Given the global economic repercussions, the United States and other adversaries of Iran would likely take military action. The United States would not be the only nation interested in resolving a dispute as quickly as possible, however, as the vast majority of supplies are delivered to Asian markets, in particular to Japan, India and China.

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Has Iran made similar threats before?

Some of those threats were intended to be rhetorical, at least in the short run. Last July, for instance, Iranian President Hassan Rouhani implied that Iran had the power to severely disrupt the oil trade in the Persian Gulf, which would likely have meant an attempt to blockade the Strait of Hormuz. Rouhani later appeared to repeat his veiled threat and was quoted on his official website as saying: “Mr. Trump! We are the people of dignity and guarantor of security of the waterway of the region throughout the history. Don’t play with the lion’s tail; you will regret it.”

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Trump eventually responded on Twitter, writing that Iran “WILL SUFFER CONSEQUENCES THE LIKES OF WHICH FEW THROUGHOUT HISTORY HAVE EVER SUFFERED BEFORE,” in case it threatened the United States.

But prior incidents have shown how serious both nations take the Strait of Hormuz, and how easily maneuvers could escalate. In 2016, Iranian naval vessels veered close to American warships in the strait, prompting a U.S. warning. “These are incidents that carry a risk of escalation, and we don’t desire any kind of escalation,” Pentagon spokesman Peter Cook warned Iran at the time.

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With more U.S. military assets headed into the region, the likelihood of an escalation has once again inched up.

This post was first published May 6. It was updated May 13.