Britain's Military Joint Headquarters at Northwood will host military planners from allied nations on April 8 to discuss long-term options for securing the Strait of Hormuz, as Trump's deadline for Iran to reopen the waterway approaches, the Press Association reported.

Trump gave Tehran until 8pm Eastern time in the US on April 8 to end its blockade or face strikes on civilian infrastructure, including power plants and bridges. He dismissed suggestions that targeting civilian facilities would constitute a war crime.

The Northwood meeting is expected to focus on plans for an international coalition to make the strait safe for shipping after a ceasefire. No deployment is likely while fighting continues, with the risk to vessels from Iranian drones and missiles currently deemed too high even by the US Navy.

The session follows a virtual meeting of more than 40 nations chaired by Foreign Secretary Yvette Cooper on April 2 that discussed collective pressure on Tehran. The UK government has pledged to stay out of any offensive action against Iran.

Trump continued to attack NATO allies at a press conference on April 7, calling the alliance a "paper tiger" and linking his frustration over allied reluctance to support the Iran war to the Greenland dispute with Denmark.

"It all began with, if you want to know the truth, Greenland. We want Greenland. They don't want to give it to us. And I said, bye bye," he said.

The president also appeared to direct personal criticism at Prime Minister Keir Starmer, comparing him to Neville Chamberlain, the British leader now remembered for appeasing Nazi Germany in the 1930s.

Starmer has repeatedly said "this is not our war" and that Britain would not be drawn into the conflict. He has instead focused on the economic fallout, warning that reopening Hormuz "will not be easy" and would require "a united front of military strength and diplomatic activity."

Iran's deputy foreign minister confirmed on April 2 that Tehran intends to impose tolls on vessels transiting the strait, with the exact rate still under review. Oil prices stood at $111 a barrel on April 7.