"The Islamic Revolutionary Guard Corps (IRGC) forcibly seized a commercial vessel possibly engaged in smuggling activity," the Bahrain-based US Navy's Fifth Fleet said in a statement.

US forces monitored the incident in international waters, it added, but "assessed the circumstances of this event did not warrant further response".

The statement did not identify the commercial ship.

"US forces remain vigilant and ready to protect navigational rights of lawful maritime traffic in the Middle East's critical waters," it said.

In recent years, Washington and Tehran have traded accusations over a series of incidents in the tense Gulf waterways that are vital to the global oil trade.

On Wednesday, the US Navy said it had blocked two attempts by the Iranian navy to seize commercial tankers in international waters off Oman, including one case in which the Iranians fired shots.

In both cases, the US Central Command said the Iranians departed after a US destroyer appeared on the scene.

The maritime services in Iran said one of the two tankers, the Bahamian-flagged Richmond Voyager, had collided with an Iranian vessel, seriously injuring five crew members, according to state news agency IRNA.

They said the collision had occurred on Tuesday and that it damaged and caused the flooding of the Iranian vessel.

"The Richmond Voyager continued on its way, regardless of international maritime rules and regulations," IRNA said, adding a court order had been issued for Iran's navy to seize the tanker.

The news agency said the tanker changed course before entering Oman's territorial waters.

Iran said it had referred the matter to the "friendly" Sultanate of Oman, which has mediated talks between the Islamic republic and the United States, and that it was seeking the vessel's seizure.

In April and early May, Iran seized two tankers within a week in regional waters.

In one case, helicopter-borne Iranian navy commandos abseiled onto the deck of a Marshall Islands-flagged oil tanker, the Advantage Sweet, in the Gulf of Oman.

Iran was also accused of launching a drone attack against an Israeli-owned tanker in November 2022, stoking tensions with the United States.

There has been a spate of such incidents since 2018, when then US president Donald Trump pulled out of the Iran nuclear deal and reimposed crippling sanctions on the Islamic republic, sending tensions soaring.

Talks aimed at reviving the accord remain stalled, but have recently resumed with Oman as an intermediary.