NATO has condemned the attack on the tanker Mercer Street, which left a Briton dead, and called on Iran to "respect its international obligations".
The US and UK have blamed Iran for the attack off the coast of Oman, which also killed a Romanian.
One or more explosive-laden drones are thought to have been flown into the tanker in the attack on 29 July.
Prime Minister Boris Johnson, who was asked yesterday if a military response was "on the table", said: "Iran should face up to the consequences of what they have done, accept the attribution that the Foreign Secretary has made.
"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."
A NATO spokesman said today: "We join allies in strongly condemning the recent fatal attack on the MV Mercer Street off the coast of Oman, and express our condolences to Romania and the United Kingdom for the losses they have suffered.
"Freedom of navigation is vital for all NATO allies, and must be upheld in accordance with international law.
"The United Kingdom, the United States, and Romania have concluded that Iran is highly likely responsible for this incident.
"Allies remain concerned by Iran's destabilising actions in the region, and call on Tehran to respect its international obligations."
Cover image: NATO.