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

While the U.S. and Israel have decimated Iran’s conventional military force, the Islamic Revolutionary Guard Corps has retained the ability to keep the strait closed with the threat of missiles, drones, mines and fast-attack boats.

Since then, most ships seeking to exit or enter have sought approval from the IRGC, which mined the main channel and created another path through its territorial waters.

Last month, the U.S. Navy began mine-clearing operations and sent two destroyers through the strait to re-establish freedom of navigation via an alternate route near Oman’s coast. That was followed by Project Freedom earlier this month to get more ships out with U.S. help, but it ended after only a few days.

Despite the short-lived effort, shipowners told Bloomberg that traffic has picked up over the last week as the U.S. military has provided assistance on how to navigate through the Strait of Hormuz.

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

A source told Bloomberg that Iranian fast boats approached a group of vessels transiting through the strait. But the Iranian boats turned away after helicopters suddenly appeared, the report said without identifying the helicopters.

Central Command didn’t immediately respond to a request for comment.

Ships that have crossed include some that had remained stranded in the Gulf since the war began as well as ships entering and exiting, according to Bloomberg. They also include ships from the UAE’s state oil giant and liquid natural gas tankers from Qatar.

To be sure, the increased ship traffic isn’t enough to save global oil markets from heading off a cliff in the coming weeks unless the strait fully reopens soon. But so far, at least a quarter of the non-Iranian ships stuck in the Gulf have left.

To sail through the strait without being detected by Iran, many ships are turning off their Automatic Identification Systems, which are navigational beacons that broadcast their positions to avoid collisions.

At the same time, 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 earlier this 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.

Of course, defying Iran’s attempt to claim of sovereignty over the strait comes with risks. The IRGC has 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.

Meanwhile, Tehran has tried to formalize control over the strait by creating 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.

“Regardless of whether a payment is made, U.S. persons are prohibited from receiving services from the Government of Iran, including services related to a guarantee of safe passage,” the Treasury Department said on Friday.