Amid simmering tensions between the Trump administration and the Iranian regime, two petrochemical tankers in the Gulf of Oman were suspected to have been targeted Thursday.

Japanese Prime Minister Shinzo Abe was in Tehran trying to negotiate between the United States and Iran when news broke that a Japanese-owned ship was among the two targets. Photos showed the other targeted vessel to be on fire.

The crews of both ships were evacuated. Both Iran and the U.S. Navy said they were assisting.

Is Iran behind the suspected attacks?

It was not immediately clear who was responsible for the suspected attacks, but they bore similarities with other incidents in the region in May, which heightened tensions between Washington and Tehran.

At the time, the Trump administration blamed Iran, but the Iranian regime denied any involvement and an inquiry led by the United Arab Emirates and co-presented by Norway and Saudi Arabia stopped short of finding conclusive evidence that Iran was behind the incidents.

The Trump administration appears to have little doubt, however, that Iran was involved and has deployed additional U.S. resources to the region.

U.S. warnings of potential Iranian attacks on vessels preceded the recent incidents. “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,” the U.S. Maritime Administration warned in May.

Among the reasons the United States is on high alert is the economic significance of 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.”

Why is the Strait of Hormuz so important?

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 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.

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

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.

Has Iran made similar threats before?

Many times, for instance in 2011, 2012, 2016 and 2018.

Some of those threats were intended to be rhetorical, at least in the short run. In 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.”

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

But earlier incidents have shown how seriously 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.

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 June 13.