Iran imposed the blockade on the critical shipping bottleneck as soon as the US and Israel launched the war against the Islamic republic on February 28, leading to a surge in global energy prices. Even with a shaky ceasefire in place, the US is now imposing its own blockade on Iranian ports.

European leaders are now worried that if the blockade continues, consumers will feel the effects through higher inflation, food shortages and flight cancellations as jet fuel runs out.

Macron and Starmer held bilateral talks at the Elysee Palace before the wider meeting got underway in the afternoon. Key EU players German Chancellor Friedrich Merz and Italian Prime Minister Giorgia Meloni attended in person in Paris with some other 30 heads of state and government joining via video conference.

The UK premier came to Paris to co-chair the event despite renewed pressure at home over the fallout from the choice of Peter Mandelson as ambassador to Washington despite his ties to late US sex offender Jeffrey Epstein.

The meeting is also a chance for Europe to display its capacities after having largely been sidelined by the US in diplomatic efforts to end the war.

According to the Elysee, the leaders will call for a return to full freedom of navigation in the strait and address the economic consequences of the blockade but also prepare the deployment of "a strictly defensive multinational military mission" to ensure freedom of navigation.

- 'Combined military effort' -

Officials have emphasised that such a force would only be deployed when the war came to an end. Key potential tasks would include mine-sweeping and ensuring no tolls are levied for passage.

"We need some military planning, and that is what we're coming together to do today, and it's the right thing to do, because the longer this conflict goes on, the more the impact," Starmer said before the meeting.

A French presidential official, asking not to be named, said allies needed to be sure "we have an Iranian commitment not to fire on passing ships and a US commitment not to block any ships leaving or entering the Strait of Hormuz."

Macron and Starmer have also led efforts to create a European force to support Ukraine, which again would only be deployed when the war against Russia ends.

The talks according to the Elysee involve "non belligerent countries" meaning that neither Iran, Israel nor the United States have been invited.

Downing Street said planning is already underway for a "combined military effort as soon as conditions allow". Military chiefs are due to meet next week for further discussions at the UK's military command headquarters in Northwood outside London, it added.

According to the French presidency, the meeting will also address concerns over the more than 20,000 seafarers aboard the hundreds of ships which have been trapped by the blockade.

Merz, whose country was initially reluctant to be involved in any mission for Ukraine, said on Thursday Berlin was "willing in principle to take part" but cautioned that "we are still very far from that".

He also added the leaders would discuss the involvement of the United States. But the French presidential official said Washington -- as a belligerent power in the conflict -- should not be involved in this mission.