The Foreign Office has said that it believes the strike on the oil tanker off the coast of Oman was “deliberate, targeted, and a clear violation of international law by Iran”.
The UK’s minister for digital infrastructure Matt Warman said on Monday that “all the evidence that we see points to the fact that it was Iranian action”.
The Iranian government has denied responsibility – but the British government warned Tehran that it was working with allies “on a concerted response to this unacceptable attack”.
Asked on Sky News what the retaliatory response might be, Mr Warman said: “It means working with those international partners. It’s right that this is a multi-lateral response.”
The strike on the MV Mercer Street tanker on Thursday night was the first known fatal attack after years of assaults on commercial shipping in the region linked to tensions with Iran over its tattered nuclear deal.
UK maritime security firm Ambrey said the attack – which saw a hole blasted through the vessel’s bridge – killed one of its British employees aboard. A Romanian national was also killed, the Foreign Office said.
British foreign secretary Dominic Raab issued a statement on Sunday afternoon condemning “the unlawful and callous attack committed on a merchant vessel off the coast of Oman, which killed a British and a Romanian national”.
The cabinet minister also said it was “highly likely” Iran had carried out a deliberate drone attack on the oil tanker. Mr Raab added: “Iran must end such attacks, and vessels must be allowed to navigate freely in accordance with international law.”
Mr Warman told Sky News that the UK government had consulted with international partners on who was behind the unmanned aerial vehicles (UAV) attack.
“All the evidence that we see points to the fact that it was Iranian action, that is I think an important thing to say publicly. Now the issue is working with those international partners to see what action can be taken,” the minister said.
“So it’s a very serious situation and one that we’d like to see the end of as quickly as possible, so Iran really does need to do better, I think, on this situation.”
The UK’s stance was supported by the US, with secretary of state Antony Blinken stating he was “confident that Iran conducted this attack”.
Israeli prime minister Naftali Bennett accused Tehran of “trying to shirk responsibility” for the attack – calling its denial “cowardly”.
Iranian foreign ministry spokesman Saeed Khatibzadeh told a weekly news conference on Sunday that the “Zionist regime [Israel] has created insecurity, terror and violence … These accusations about Iran’s involvement are condemned by Tehran”.
Labour Party’s shadow foreign secretary Lisa Nandy has urged Boris Johnson’s government to “make it clear” to the incoming Iran president Ebrahim Raisi – a protege of Supreme Leader Ayatollah Ali Khamenei – that the killing of a British national will “carry costs”.
The MV Mercer Street tanker is managed by London-based Zodiac Maritime, part of Israeli billionaire Eyal Ofer’s Zodiac Group. The vessel had been on its way from Tanzania to the United Arab Emirates at the time of the attack.
The American nuclear-powered aircraft carrier USS Ronald Reagan and the guided missile destroyer USS Mitscher were escorting the MV Mercer Street as it headed to a safe port, the US navy’s Middle East-based 5th Fleet said in a statement on Saturday.
It said navy explosive experts believed a drone attacked the vessel. The drone attack blasted a hole through the top of the oil tanker’s bridge, where the captain and crew command the vessel, a US official said.