The ship, which had left Ajman in the United Arab Emirates destined for Singapore, was heading for Iranian waters.

Ellie Shafik of Vanguard Tech told AFP the Talara had been intercepted by Iran's Revolutionary Guards (IRGC) and detained.

"It's unclear why," she said. "Iran will likely frame this as a judicially ordered, law-based action, masking what may just be a strategic seizure."

Iran has so far not commented on the incident.

The US Navy said it was "actively monitoring the situation".

"Commercial vessels are entitled to largely unimpeded rights of navigation and commerce on the high seas," said the US 5th Fleet, which patrols the region.

The Marshall Islands-flagged vessel was heading south through the Strait of Hormuz when it was approached by three small boats, maritime security company Ambrey said, adding it had made a "sudden course deviation".

Maritime Security company Neptune P2P Group said the vessel had been seized by "suspected Iranian forces".

"The incident appears to be the latest in a series of illegal ship seizures transiting the Strait of Hormuz and Gulf of Oman in recent years, but it is the first since the seizure of the commercial ship MSC ARIES in April 2024," it said in a note.

"The Islamic Revolutionary Guard Corps Navy are usually responsible for such incidents and has been known to use such activity to apply political pressure in the region," it added.

The British Royal Navy-run UKMTO, meanwhile, said the incident was "believed to be state activity".

The Strait of Hormuz, a major conduit for global oil and liquefied natural gas, has previously been the scene of similar incidents.

Last year, Iran's Revolutionary Guard seized a container ship, saying it had links to Israel, following a deadly attack on Iran's consulate in Syria blamed on Israel.