Britain, France, Germany, Italy, Japan and the Netherlands said they were ready "to contribute to appropriate efforts to ensure safe passage through the Strait of Hormuz," though three stressed any initiative would only take place with a ceasefire in place.

The grouping said they "welcome the commitment of nations who are engaging in preparatory planning" as they condemned "in the strongest terms recent attacks by Iran on unarmed commercial vessels in the Gulf."

But Italy, Germany and France made clear late on Thursday that they were not talking about any immediate military help, but rather a potential multilateral initiative after a truce.

The declaration came as an effective Iranian blockade of the strait has paralyzed commercial shipping through the crucial maritime chokepoint, which in peacetime sees a fifth of global crude oil and liquefied natural gas pass through it.

The war, which erupted on February 28 when the United States and Israel began bombing Iran, has led Tehran to retaliate with strikes across the Gulf region.

Twenty-three commercial vessels, including 10 tankers, have reported incidents or having been attacked. The situation has left around 20,000 seafarers stranded on approximately 3,200 vessels west of the strait, according to the International Maritime Organization.

"We express our deep concern about the escalating conflict," the allies' joint statement said. "We call on Iran to cease immediately its threats, laying of mines, drone and missile attacks and other attempts to block the Strait to commercial shipping.

"Freedom of navigation is a fundamental principle of international law, including under the UN Convention on the Law of the Sea. The effects of Iran's actions will be felt by people in all parts of the world, especially the most vulnerable." 

Not a 'war mission'

US President Donald Trump has urged other world powers, and NATO, to help reopen the Hormuz Strait to commercial shipping. But they have rebuffed his call in the short term while insisting they were open to discussions and planning.

Italy's Defense Minister Guido Crosetto said the statement by the six countries should not be seen as a "war mission". "No entry into Hormuz without a truce and a comprehensive multilateral initiative", for which "it is right and appropriate for the UN to provide the legal framework," he said in a statement.

And in Berlin, Defense Minister Boris Pistorius said any German military involvement "would depend on the situation after a ceasefire and whether we could participate within the framework of an international mandate".

Military involvement would also require approval by the German parliament, he added.

French President Emmanuel Macron said his country planned to sound out permanent members of the UN Security Council on the possibilty of establishing a UN framework for future plans - once the ongoing exchange of fire had ended - to secure navigation in the Strait of Hormuz.

"We have initiated an exploratory process, and we will see in the coming days whether it stands a chance of succeeding," he said in Brussels following Thursday's European summit.

Peace ambitions

China said will continue to strengthen communication with all relevant parties on the US-Israel conflict with Iran in an attempt to mediate a truce.

Speaking in Beijing on Friday, Foreign Ministry spokesman Lin Jian said: "The current conflict in the Middle East is escalating, and the war is expanding, which not only impacts regional peace and stability, but also directly affects international energy, finance, trade and shipping, undermining the common interests of all countries. 

"History and reality have repeatedly proven that force provides no solution, and armed conflict will only add new hatred. The parties involved should immediately stop military operations to prevent further deterioration of situation. 

"China will continue to strengthen communication with all relevant parties to mediate a ceasefire, so that peace and stability will be restored in the Middle East at an early date."

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