That alternate channel has become even more important after Iran vowed Monday to completely close the strait in response to ongoing Israeli attacks in Lebanon. Brent crude prices jumped 7% to $97.32 a barrel.

Over the last three weeks, Central Command has guided about 70 ships in and out of the Persian Gulf, sources told the New York Times, indicating that the route was not close to the Iranian coastline.

That rules out the lane the Islamic Revolutionary Guard Corps established soon after the U.S. and Israel launched their war on Iran. Since then, the IRGC has charged tolls on ships granted permission and attacked any that tried to cross unauthorized.

To bypass the IRGC-controlled lane, the U.S. Navy began mine-clearing operations in April and sent two destroyers through the strait to re-establish freedom of navigation via another route near Oman’s coast. That was followed by Project Freedom last month, which aimed to get more ships out with U.S. help, but it ended after only a few days.

To sail through the strait without being detected by Iran, most of the ships crossing via the U.S. channel are turning off their Automatic Identification Systems, according to the Times.

The AIS is a navigational beacon that broadcasts its position to help avoid collisions. By going dark, ships must rely on guidance from Central Command.

Central Command has insisted that it’s not escorting ships. Instead, it’s offering advice to commercial vessels in the region.

The U.S. military keeps an eye on traffic with radar, drones and other tools to help ships transit safely, while also advising them on when to turn off AIS and how to respond to Iranian threats, sources told the Wall Street Journal.

A Greek supertanker carrying 2 million barrels of crude oil crossed the strait in this manner last week, using the route near Oman’s coast, according to the report. A Chinese-owned vessel loaded with fertilizer also exited recently along the Omani coast.

Oil supplies and ships trapped

Shipowners told Bloomberg that traffic picked up over the past week with U.S. assistance, adding that Iranian fast boats approached a group of vessels transiting through the strait, but turned away after helicopters suddenly appeared.

The report didn’t identify the helicopters, and Central Command declined to comment when asked if they were from the U.S. military.

The trickle of traffic comes as the strait has been effectively shut for three months, keeping one-fifth of the world’s oil supplies as well as 2,000 ships trapped in the Persian Gulf.

But at least a quarter of the non-Iranian ships stuck in the Gulf have left since the war started. And according to maritime data company Kpler, 895 ships crossed the strait between March 1 and May 19, with just over half going through Iran’s route and about 40% taking an unknown route.

Meanwhile, Tehran has been making a point of announcing how many ships are crossing with its approval. On Monday, the IRGC said 15 ships, including four oil tankers, passed through. It also released a video showing fast-attack boats patrolling the strait.

Tehran has sought to formalize its control over the strait by establishing the Persian Gulf Strait Authority. But the U.S. sanctioned it and warned that any deals with Iran to sail through the Strait of Hormuz are forbidden.

Strait challenges ceasefire

Jockeying over the strait has stoked more fighting in the Gulf, testing the fragile ceasefire between the U.S. and Iran.

Last month, the IRGC launched attacks into the Gulf and attempted to lay new underwater mines. The U.S. responded by destroying Iranian boats and bombing missile sites in Iran that tried to shoot down U.S. aircraft.

Over the weekend, the U.S. disabled a ship attempting to breach its naval blockade by firing a missile into the engine room. Also this weekend, the U.S. conducted “self-defense strikes” in Goruk, Iran, and Qeshm Island.

After Iran shot down a U.S. drone, fighter aircraft destroyed Iranian air defenses, a ground control station, and two one-way attack drones that threatened ships in transit, Central Command said.

And on Monday, the U.S. said it successfully intercepted two Iranian ballistic missiles targeting American forces based in Kuwait.

Rapidan Energy founder Bob McNally, who previously served as White House energy advisor to President George W. Bush, suggested in April that the Iranian threat need not be completely eliminated for traffic to return to the strait.

“You may not perfectly get rid of it, but degrading Iran’s ability to interdict shipping down to a manageable level—that’s when insurance can come into play and escorts, and folks can start to move through,” he told CNBC.