Iranian forces boarded a tanker in international waters in the Gulf of Oman, using a helicopter and two ships to take over the vessel for several hours, US officials said.
They also posted grainy black-and-white footage of the helicopter hovering low over the vessel and special forces personnel fast-roping onto the deck.
"Today in international waters, Iranian forces, including two ships and an Iranian 'Sea King' helicopter, overtook and boarded a ship called the 'Wila'," US Central Command said in a Wednesday (August 12th) social media post.
A US defence official said the Iranians released the vessel, a Liberian-flagged oil and chemicals tanker, after holding it for four to five hours.
The incident occurred in international waters of the Gulf of Oman, just 32 kilometres off the coast of the UAE.
"Iranian special forces fast roped from the Sea King on to the ship," the US official said Thursday. "A coalition ship monitored the event but did not receive a distress call from M/T Wila."
Bloomberg said the vessel had been floating off the eastern coast of the UAE for the past month, but that it appeared to have picked up a shipment in July near the Iraqi oil terminal of al-Basra.
The waters where the ship was boarded, near the Strait of Hormuz, are a chokepoint for a third of the world's seaborne oil.
Possible link to sanctions
Maritime security analysts Dryad Global on Wednesday said there are indications that the tanker may have been targeted as a result of a previous linkage to Greek companies sanctioned by the US in June.
The US Department of Justice sanctioned the companies for their intended involvement in an Iranian oil shipment to Venezuela.
"Greek-managed vessels have come to the fore in recent months following their willingness to trade oil exported from Iran to Venezuela," Dryad Global said.
"Such a move brought Greek-firms under international scrutiny, and in June of this year four vessels linked to Greek companies were blacklisted by the US. Following this blacklisting, future shipments of crude oil from Iran which were to be carried by Greek-managed vessels were scrapped."
"If confirmed, it is likely that this decision has raised Iran's ire, and that Iran has waited for an opportune moment when it can respond."
"In targeting this vessel, Iran has potentially sought to send a clear message to vessels which decide to renege on their willingness to partake in, or facilitate, economic activities linked to the nation," Dryad Global said.
"Iran also has a domestic environment which provides ample reason to seek outside distractions," the maritime security analysts added, pointing to its economic woes and its struggle to contain the coronavirus crisis.
"Undertaking such an action now can help to displace and refocus growing public grievance within Iran," it said.
Risk to vessels remains
While Dryad said Iran's actions "do not raise the overall risk posed by vessels within either the Gulf of Oman or Strait of Hormuz", a risk remains to vessels linked to nations embroiled in geopolitical and economic stand-offs with Iran.
In late July, Iran conducted a military exercise in Gulf waters near the Strait of Hormuz that the US Navy described as "irresponsible and reckless".
Military experts in the region called the "Prophet Mohammed 14th" land, air and sea drill "a predictable provocation" and warned of the impact on global trade.
The escalation of Iran-US tensions last year saw ships mysteriously attacked, drones downed and oil tankers seized in the strait.
In July 2019, the IRGC seized British-flagged oil tanker Stena Impero in the waterway, releasing it two months later.
The IRGC seized at least six other ships last year over alleged fuel smuggling.