The US blames Iran for a series of attacks on ships, including an attempt to seize the British Heritage tanker which was only foiled by the presence of HMS Montrose, which was escorting the ship – an incident Iran denied had taken place. Meanwhile Britain has confirmed the vessel in question was not sailing under a UK flag – maritime law means ships can be registered in a particular country even if its owners are based elsewhere. Washington said it was aware of the report but had no evidence “at this time to suggest Iran’s claims are true”.
A senior US administration official said: “The United States will continue to work with our allies and partners to safeguard global commerce and support freedom of navigation.”
It remains unclear whether the impounded ship was the same vessel Iran towed to safety on Sunday after sending a distress signal.
Iranian state television had earlier said it was the same ship but the Revolutionary Guards statement did not confirm that.
The Guards said the impounded ship was smuggling one million litres of fuel in the area of Larak Island in the Gulf and had 12 foreign crew.
Oil prices rose after news of the seizure amid rising tensions between Tehran and the West over the safety of shipping in the Strait of Hormuz, a vital gateway for energy exports.
Brent crude futures were up 54 cents at $64.20 a barrel by 1230 GMT after hitting a session high of $64.46.
Shipping companies were reported to be hiring unarmed security guards for voyages throughout the Gulf as an extra safeguard.
Although Iran has yet to name the vessel, shipping industry sources said they believe it to be the MT Riah, a ship flying under the flag of Panama.
Refinitiv Oil Research data showed that the last signal received from the vessel was on Sunday when it was in the Strait of Hormuz off the Iranian island of Qeshm, heading towards Oman from Larak Island.
Giorgos Beleris, Oil Research Manager for Refinitiv, said: “The MT Riah has been fairly consistent with her Automatic Identification System (AIS) pings in the last three months so the fact that she went dark makes it very interesting.
“Strangely, although she’s small and can easily dock she appears to have been operating at anchorages possibly loading from other vessels via ship-to-ship.
“This could hint at something potentially shady – we can’t be certain.”
Britain said on Thursday the tanker in question was not British-flagged.
A Government spokesman said: “We are not currently aware of any UK interests in this vessel.”
Tensions with Iran have been escalating even since US President Donald Trump pulled his country out of the Joint Plan of Comprehensive Action (JPOCA) deal last year, accusing Tehran of violating the agreement.
The US has since imposed tough new sanctions on Iran targeting its oil exports.