The situation remains unclear but suspicion fell on Iran due to the vessel’s history of being seized in a dispute between Tehran and the US, with one million barrels of crude oil seized.

An oil tanker was boarded by “armed unauthorised persons” in military uniforms and masks on Thursday morning off the coast of Oman.

The situation remains unclear but suspicion immediately fell on Iran, as the vessel was once involved in a dispute with the US Justice Department that saw a million barrels of Iranian crude oil seized.

The United Kingdom Maritime Trade Operations (UKTMO), which provides warnings to sailors in the Middle East, said the incident began early in the morning 50 miles off the coast of Oman.

UKTMO described receiving a report from the ship’s security manager of hearing “unknown voices over the phone” alongside the ship’s captain.

It said it was unable to make further contact with the vessel and that the authorities were investigating the incident.