Israel has blamed Iran for a suspected drone attack on a tanker in the Arabian Sea that killed two crew, including a British national, and has vowed a harsh response. The Liberian flagged Mercer Street, which is linked to an Israeli tycoon, was hit off the coast of Oman late on Thursday in what is thought to have been a swarm attack involving multiple drones. The strike appeared to fit a pattern of previous attacks on maritime traffic linked to Iran and Israel carried out in a shadow war between the two foes. The Israeli foreign minister, Yair Lapid, said on Friday night that he had contacted Dominic Raab, his UK counterpart. “Iran is not just an Israeli problem, but an exporter of terrorism, destruction and instability that harms us all,” he said. “The world must not be silent in the face of Iranian terrorism that also harms freedom of shipping.” Though Mercer Street is Japanese owned, it is managed by an Israeli-owned company, Zodiac Maritime, part of the billionaire Eyal Ofer’s Zodiac Group, which acknowledged the deaths and initially described the incident as piracy. The other victim was a Romanian national, the firm said. The piracy claim was later rejected by regional officials. The regional high seas have been the scene of an estimated 150 or more strikes over the past three years, in Gulf waters, the Red Sea and the eastern Mediterranean coast, many of which have remained unacknowledged by either side. Drones have been increasingly used by both sides throughout this year. Earlier, mines placed on ship hulls and occasionally small rockets are believed to have been deployed in incidents that damaged dozens of ships. While disruption to shipping has been common, deaths have been rare. A drone strike believed to have been carried out on an Iranian oil tanker off the Syrian coast in the spring killed three people when a missile burst through the vessel’s bridge. In June, the biggest ship in the Iranian navy sank near Oman after its engine room mysteriously caught fire. Mayday calls were detected in nearby Oman and in Saudi Arabia on Thursday night. The US navy is believed to have escorted the Mercer Street to the Omani island of Masirah. The British military’s United Kingdom Maritime Trade Operations said an investigation was under way into the attack and that coalition forces were taking part. A US official told Associated Press the attack appeared to have been carried out by a “one-way” drone and other drones took part. The official said it was not immediately known who launched the attack. A UK government spokesperson said: “Our thoughts are with the loved ones of a British national who has died following an incident on a tanker off the coast of Oman. “Vessels must be allowed to navigate freely in accordance with international law. We are working with our international partners to urgently establish the facts.” The Ministry of Defence said: “We are aware of reports of an attack on a merchant vessel off the coast of Oman. UK military headquarters in the region are currently conducting investigations.” The British maritime security firm Ambrey said the attack had killed one of its team members, along with a member of the tanker’s crew. “It is with deep regret that I can confirm that an Ambrey team member has tragically been killed in a security incident,” the company said on Friday. “The incident occurred in the northern Indian Ocean onboard the product tanker M/T Mercer Street. We can confirm a member of the crew was also killed. “We are currently working closely with our client and the relevant authorities, whilst offering all the support possible to the victim’s next of kin. Our thoughts are with the family and friends of those involved at this incredibly sad time.” Iranian and Houthi rebels in Yemen backed by Tehran have increasingly deployed drone swarm technology against regional foes. In May 2019, half of Saudi Arabia’s oil production capacity was taken offline for several weeks when multiple drones targeted the country’s main production facility. Washington and Riyadh believe the attack was launched from the Iranian side of the border with Iraq, close to Gulf waters. The incident came as talks between Tehran and Washington to reactivate the nuclear deal continued to stall. Hours before the strike, the US had declared its frustration with the slow pace of the Vienna-based negotiations, which would lift sanctions reimposed by Donald Trump after his predecessor Barack Obama lifted them during his second term as US president. The Mercer Street was travelling from Dar es Salaam in Tanzania to Fujairah in the United Arab Emirates with no cargo onboard. It is the second vessel linked to the Israeli tycoon to have been targeted this month. The first, the container ship CSAV Tyndall, suffered damage from an unexplained explosion in the Indian Ocean. “With profound sadness, we understand the incident onboard the M/T Mercer Street on 29 July 2021 has resulted in the deaths of two crew members onboard: a Romanian national and a UK national,” Zodiac Maritime wrote on Twitter. “We are not aware of harm to any other personnel.” The deaths are likely to spark a more significant response in coming days than the dozens of prior strikes, which caused only material damage. The shadow conflict between Iran and Israel has been fought on regional waterways and from the skies above Syria and Iraq, where Israeli jets have routinely bombed targets that Israel believes are linked to Iran. Whether on land, or water, neither side typically claims responsibility for the strikes it launches, preferring a series of low-key tit-for-tat responses and an absence of rhetoric that could lead to any escalation.