Britain has summoned the Iranian ambassador to London for a meeting at the Foreign Office, accusing Tehran of an “unlawful” drone attack that killed a British citizen on a ship off Oman last week. James Cleverly, a Foreign Office minister, stressed to Mohsen Baharvand, the ambassador, that Iran must “immediately cease actions that risk international peace and security”, and said “vessels must be allowed to navigate freely in accordance with international law”. The UK has said it was highly likely that Iran carried out an “unlawful and callous attack” on a ship in the Middle East, which left a Briton and a Romanian dead. Whitehall sources said the UK was currently considering its diplomatic response and how to retaliate, but the first step was seeking international agreement that Iran was behind the attack from bodies such as the United Nations and the G7. Speaking on a visit to Airbus in Stevenage, Boris Johnson said: “I think that Iran should face up to the consequences of what they have done, accept the attribution that the foreign secretary has made. “This was clearly an unacceptable and outrageous attack on commercial shipping; a UK national died. It is absolutely vital that Iran and every other country respects the freedoms of navigation around the world, and the UK will continue to insist on that.” 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 nuclear deal. The British maritime security firm Ambrey said the attack killed one of its employees aboard the vessel. A Romanian crewmember also died. Iran has denied responsibility after Israel’s prime minister, Naftali Bennett, directly blamed it for the attack. Dominic Raab, the foreign secretary, said the UK government backed Bennett’s claim. He said the government believed the drone attack off the coast of Oman was “deliberate, targeted, and a clear violation of international law by Iran”. On Monday, Matt Warman, the minister for digital infrastructure, told Sky News: “Well, working with international partners of course, 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, and now the issue is working with those international partners to see what action can be taken. But it’s clearly totally unacceptable for any state to be taking the kind of action that results in the loss of life, in this case the loss of two lives, one of them British. “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. “It means working with those international partners … UIt’s right that this is a multilateral response. There isn’t an announcement today, but I think you would see that that announcement attributing the attack to Iran is part of a step on a road that we think will involve multilateral responses.”