‘This is the last warning.’ Iran threatened US warships after throwing down the gauntlet to conquer the Strait of Hormuz

US Navy ships sent an unmistakable signal on Saturday as they passed through the Strait of Hormuz, challenging Iran’s control of the narrow waterway that will determine the outcome of the Middle East war.

USS Michael Murphy It and another destroyer, the USS, opened its automatic identification system Frank E. Petersontransited the strait, breaking the typical protocol of naval vessels having their AIS turned off.

“You don’t accidentally throw an AIS on a naval ship,” Campbell University professor Salvatore Mercogliano, who specializes in military and maritime history, said on his podcast. “It’s purposeful. They wanted to open it at the far end of the Strait of Hormuz that they’ve sailed.”

US Central Command said destroyers had begun setting conditions for clearing mines laid by Iran’s Islamic Revolutionary Guard Corps.

It said more US forces, including underwater drones, would join the clearance effort in the coming days, pointing out that the strait is an international sea route and an essential trade corridor.

In a statement, Admiral Brad Cooper said Central Command is “establishing a new path” for the maritime industry for the free flow of commerce.

Before the war, Iran’s grip on the strait, through which one-fifth of the world’s oil and liquid natural gas flows, has fueled the global energy crisis and represents a key form of regime leverage over the US.

The disastrous crossing of the strait comes after the US and Iran began ceasefire talks in Pakistan this weekend. But if the Navy creates a safe passage for tankers that don’t have to get Iran’s permission and pay tolls, the negotiations will shift in America’s favor.

As a result, the IRGC challenged naval destroyers in transit, according to a radio conversation recorded by a civilian ship. The Wall Street Journal.

“This is a final warning. This is a final warning,” the IRGC said.

“Passed in accordance with international law. You intend no challenge, and I intend to abide by the terms of our government’s armistice,” replied the American ship.

Iranian media said the destroyers turned back after being confronted by the IRGC, which reportedly launched a drone in the direction of the destroyers. The IRGC also said any attempt by military vessels to cross the strait would be met with a “stern and strong response”.

Until now, US warships have avoided the strait as naval officials have previously described it as an Iranian “kill box” filled with myriad threats, including anti-ship missiles, drones, fast-attack boats, and mines. And given how narrow the strait is, projectiles can be fired at close range and provide little time for a defensive reaction.

Meanwhile, the US military continues to send more combat power to the region. A third aircraft carrier, along with thousands of Marines and paratroopers, is expected to arrive later this month. Several long-range cruise missiles are also floating in the Middle East.

Mercogliano said there were earlier indications that the Navy resupplied its ships through Diego Garcia Island, potentially to replenish weapons. Littoral combat ships equipped with mine-hunting underwater drones may also be in the mix.

Although it is unclear whether the destroyers entered the strait with those ships or without them, it is still an important milestone for the oil trade.

“One of the things the commercial ships are waiting to see is whether the strait is clear, and two destroyers going in is a big deal,” he added.

Despite ongoing cease-fire talks, another military clash between the US and Iran could be imminent. Rapidan Energy founder Bob McNally told CNBC on Thursday that he thinks the U.S. is “getting ready for Round 2.”

As the U.S. weakens Iran’s ability to threaten shipping traffic, Iran’s leverage will decrease and a full reopening of the Strait of Hormuz could be conditions for a permanent ceasefire by the end of this month, he said.

McNealy likened ignoring Iran’s threats to a game of hack-a-mole, given the diversity of its weapons, and pointed out that the U.S. has depleted Iran’s stockpile of underwater mines.

“It may not be widely reported, but I believe the US military has been focusing on hitting those moles for the last week or so, to reduce Iran’s capabilities,” he added. “You can’t get rid of it completely, but it can reduce Iran’s ability to stop shipping at a manageable level — and that’s when insurance can come into play and escort, and people can start going through.”

This story was originally featured on Fortune.com