NATO allies have rejected a US proposal to blockade Iranian ports, saying they would only consider intervening once fighting ends, a stance that will likely anger Washington and further strain the alliance.

After talks failed over the weekend to end the six-week conflict with Iran, the United States said its forces would destroy any Iranian ships approaching the blockade, which began on Monday.

Citing the need to avoid escalation, NATO allies, including the United Kingdom and France, said they would not join the blockade and were instead working on a plan to open the strait, Reuters reported.

UK Prime Minister Keir Starmer said on Monday that his country would neither be drawn into a war with Iran nor take part in a blockade of the Strait of Hormuz.

The White House has threatened to leave the NATO alliance and is reportedly considering pulling some troops from Europe, after some countries barred US military flights from their airspace for strikes on Iran.

Last week, NATO Secretary-General Mark Rutte said the bloc could take on a role in the strait if all 32 allies agree to establish a mission.

Governments across Europe say they are prepared to help in the strait, but only after an end to hostilities and assurances from Iran that their ships will not be targeted.

French President Emmanuel Macron's office said on Tuesday that France and the UK will cohost a conference on Friday of nations ready to contribute to a "purely defensive mission" to secure the Strait of Hormuz.

Starmer told Parliament on Monday that the initiative would set rules for safe passage and the coordination of naval escorts for tankers.

"Let me be very clear, this is about safeguarding shipping and supporting freedom of navigation once the conflict ends," he said. "Our shared aim here is a coordinated, independent, multinational plan."

Spain's Foreign Minister Jose Manuel Albares said last week that securing passage through the Strait of Hormuz is beyond the remit of the NATO alliance, after the White House vented frustration at its lack of action on the vital waterway.

"NATO has no involvement in this war. We, the allies, have not been informed or consulted," Albares told the Spanish Senate on Friday.

"Not only us, but many allies have expressed the same sentiment — NATO will not participate in this war."

Turkiye's Trade Minister Omer Bolat said last week that the alliance is not obliged to intervene and allies are not obliged to assist the US and Israel in their war with Iran.