The UK has said it is “highly likely” Iran carried out an “unlawful and callous attack” on a ship in the Middle East which left a Briton dead.

Foreign Secretary Dominic Raab said the Government believed the drone attack on the oil tanker off the coast of Oman was “deliberate, targeted, and a clear violation of international law by Iran”.

The strike on the oil tanker Mercer Street 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.

British maritime security firm Ambrey said the attack, which saw a hole blasted through the vessel’s bridge, killed one of its employees aboard.

Iran denied responsibility after Israel’s prime minister directly blamed it for the attack, but Mr Raab said the UK Government backed Naftali Bennett’s claim.

“The UK condemns the unlawful and callous attack committed on a merchant vessel off the coast of Oman, which killed a British and a Romanian national,” said the Cabinet minister.

“Our thoughts are with the friends and family of those killed in the incident.

“We believe this attack was deliberate, targeted, and a clear violation of international law by Iran.

“UK assessments have concluded that it is highly likely that Iran attacked the MV Mercer Street in international waters off Oman on July 29 using one or more unmanned aerial vehicles (UAVs).

“Iran must end such attacks, and vessels must be allowed to navigate freely in accordance with international law.

“The UK is working with our international partners on a concerted response to this unacceptable attack.”

On Sunday night, Labour shadow foreign secretary Lisa Nandy urged the Prime Minister to “make it clear” to Iran that the incident would “carry costs”.

In a statement, Ms Nandy said: “This reckless Iranian attack on a merchant vessel in international waters is a flagrant breach of international law.

“It is tragic that this has led to the death of two sailors, including one Briton. We send our deepest condolences to their families.

“The Prime Minister must make it clear to the incoming Iranian President that lawless actions will carry costs.

“This is the moment where Britain must show we are resolute in our determination to end this pattern of behaviour.

“The breakdown of a clear strategy to deal with Iran has not served the UK or our allies well in recent years. The Foreign Secretary must now make it a priority to pursue coordinated international efforts to tackle these actions by the Iranian Government.”

At least three other Israeli-linked ships have been attacked in the region - including MV Helios Ray, MV Hyperion Ray and CSAV Tyndall - this year. The Foreign Office said the drone assault followed similar attacks on three other Israeli-linked ships in the region since February.

Speaking earlier this week at a Cabinet meeting in Jersusalem, Mr Bennett blamed Iran for the drone attack.

“The intelligence evidence for this exists and we expect the international community will make it clear to the Iranian regime that they have made a serious mistake,’ the Israeli premier said at the weekly cabinet meeting in remarks conveyed by his office.

“In any case, we know how to send a message to Iran in our own way.”

Israeli Foreign Minister Yair Lapid said: “[I] noted to [Mr Raab] the need to respond severely to the attack. Iran is not just an Israeli problem, but an exporter of terror, destruction and instability that hurt us all. The world must not be silent in the face of Iranian terror.”

The Mercer Street is managed by London-based Zodiac Maritime, part of Israeli billionaire Eyal Ofer’s Zodiac Group.

Iranian Foreign Ministry spokesman Saeed Khatibzadeh, responding to Israel’s accusations, described the allegation that Iran carried out the attack as “baseless”.

The Mercer Street, empty of cargo, had been on its way from Dar es Salaam, Tanzania, to Fujairah, United Arab Emirates, at the time of the attack, Zodiac Maritime said.

The attack targeted the tanker just north east of the Omani island of Masirah, 185 miles south east of Oman’s capital Muscat.

The American nuclear-powered aircraft carrier USS Ronald Reagan and the guided missile destroyer USS Mitscher were escorting the 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.

The official spoke on condition of anonymity as an investigation into the attack was still ongoing.

Zodiac Maritime said the Mercer Street’s owners are Japanese, without naming them.

Shipping authority Lloyd’s List identified the vessel’s ultimate owner as Taihei Kaiun, which belongs to Tokyo-based Nippon Yusen Group.