Iran's ambassador has been summoned to the Foreign Office following a drone attack on an Israeli-linked oil tanker in which two crew, including a British national, were killed.
The ambassador was summoned this morning for a meeting with minister James Cleverly.
"Minister Cleverly reiterated that Iran must immediately cease actions that risk international peace and security, and reinforced that vessels must be allowed to navigate freely in accordance with international law," a spokesperson said.
The UK and US have blamed Iran for the attack on the Israeli-linked oil tanker, in which two crew members - a British national and a Romanian citizen were killed.
The attack happened last Thursday when the MV Mercer Street was off Oman's Coast in the Arabian Sea.
The strike on the 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 between Israel and Iran.
Foreign Secretary Dominic Raab accused Iran of carrying out a "deliberate, targeted" assault which constituted "a clear violation of international law".
US Secretary of State Anthony Blinken said he was considering "next steps" with the UK and other allies, with "an appropriate response... forthcoming".
The meeting with James Cleverly follows a weekend of discussions with high-level officials on how best to respond to the incident.
The head of the British armed forces, General Sir Nick Carter, held discussions with his Israeli counterpart on Sunday.
Meanwhile, the government held a Cobra emergency meeting at the level of officials over the weekend in a sign of the serious focus on the tanker attack, Sky News understands.
There's not yet been a Cobra attended by ministers, which is what happens in the gravest of crises.
The Mercer Street tanker is managed by London-based Zodiac Maritime, part of Israeli billionaire Eyal Ofer'sZodiac Group.
Earlier this week, Israeli foreign minister Yair Lapid blamed "Iranian terrorism" for the attack.
Iran has not yet commented on the allegations.