Oman on Wednesday identified the Panama-flagged Asphalt Princess as the tanker involved in a hijacking which Britain's maritime trade agency earlier said was over.
The statement by Oman's Maritime Security Centre was the first official confirmation of Tuesday's incident in the Arabian Sea which maritime security sources had told Reuters involved suspected Iranian-backed forces. Iran denied any involvement.
The United Kingdom Maritime Trade Operations (UKMTO) said in a warning notice based on a third-party source on Wednesday that people who had boarded a tanker involved in a "potential hijack" had since left and that the vessel, which it did not identify, was safe.
The AIS tracking status of the asphalt/bitumen tanker Asphalt Princess was "Underway Using Engine" early on Wednesday, according to Refinitiv ship tracking data.
The Oman Maritime Security Centre said in a statement it had received information about the Asphalt Princess being subjected "to a hijacking incident in international waters in the Gulf of Oman", but gave no further details.
"The Royal Air Force of Oman is carrying out sorties near the area, and the Royal Navy of Oman deployed several ships to help secure international waters in the region," it added.
The boarding took place in an area in the Arabian Sea leading to the Strait of Hormuz, the conduit for about a fifth of the world's sea-borne oil exports.
Iran's senior armed forces spokesman, Abolfazl Shekarchi, on Tuesday denounced reports of maritime incidents and hijacking in the Gulf area as "a kind of psychological warfare and setting the stage for new bouts of adventurism".
Tensions have simmered in the region after a suspected drone attack last week on an Israeli-managed tanker off the Omani coast killed two crew and was blamed on Iran by the United States, Israel and Britain. Iran denied responsibility.
The United States and Britain have said they would work with allies to respond to the attack on the Mercer Street, a Liberian-flagged, Japanese-owned petroleum product tanker.
Tehran has said it would respond to any threat against its security.
Regional tensions have worsened since 2018, when Washington re-imposed sanctions on Iran after abandoning a 2015 nuclear deal between Tehran and global powers.