Britain said on Sunday it believed Iran carried out an attack on an Israeli-managed petroleum product tanker off the coast of Oman on Thursday that killed a Briton and a Romanian, and said it was working with partners on a "concerted response".
UK assessments had concluded that it was highly likely that Iran had used one or more drones to carry out the "unlawful and callous" attack, Reuters quoted British Foreign Secretary Dominic Raab as saying.
"We believe this attack was deliberate, targeted, and a clear violation of international law by Iran," he said on Sunday. "The UK is working with our international partners on a concerted response to this unacceptable attack."
Israeli Prime Minister Naftali Bennett had accused Tehran of "trying to shirk responsibility" for the attack, and called its denial "cowardly".
The Briton and Romanian were killed in the incident involving the Mercer Street, a Liberian-flagged, Japanese-owned ship managed by Israeli-owned Zodiac Maritime.
The US Navy, which was escorting the tanker with its aircraft carrier USS Ronald Reagan, said on Saturday that early indications "clearly pointed" to a drone attack.