*Iran will protect Gulf waters: Zarif

France, Italy and Denmark gave initial support for a British plan for a European-led naval mission to ensure safe shipping through the Strait of Hormuz, three senior EU diplomats said on Tuesday after Iran's seizure of a British-flagged tanker.

The backing at a meeting of EU envoys in Brussels contrasts sharply with the lukewarm response shown by European allies to a similar American call first voiced at NATO in late June, when countries feared they could make US-Iranian tensions worse.

"Britain's request, rather than Washington's, makes it easier for Europeans to rally round this," one senior EU diplomat said. "Freedom of navigation is essential, this is separate from the US campaign of maximum pressure on Iran."

Britain tested the idea to senior EU diplomats at a meeting in Brussels, saying it would not involve the European Union, NATO or the United States directly, the diplomats said. It was the first formal European meeting since British foreign minister Jeremy Hunt outlined the plans to parliament on Monday.

British foreign ministry and defence officials have also discussed a possible mission, which would likely involve not just ships but aircraft too, directly with their Italian, Spanish, French and German counterparts.

A senior German diplomat in Berlin said Foreign Minister Heiko Maas was in close contact with his British and French counterparts, Hunt and Jean-Yves Le Drian, to "contribute to the security" of the Gulf including on maritime security.

The Netherlands is also assessing the British proposal.

They aim to have further meetings with Madrid and Stockholm, the diplomats said, while at the EU meeting in Brussels, Sweden, Poland and Germany also showed interest.

The mission to protect vital Middle East oil shipping lanes could be run by a joint Franco-British command, one of the envoys said.

Any mission would still need parliamentary approval in some EU countries, diplomats said.

Meanwhile, Iran warned Britain's next prime minister Boris Johnson that it will "protect" waters of the oil-rich Gulf, amid a standoff between the two countries over the seizure of tankers.

In the face of rising hostilities with the United States, Iran's Islamic Revolutionary Guards on Friday impounded a tanker sailing under the flag of US ally Britain.

The seizure of the Stena Impero has been seen as a tit-for-tat move after British authorities detained an Iranian tanker on July 4 in the Mediterranean on suspicion it was shipping oil to Syria in breach of EU sanctions.

"Iran does not seek confrontation. But we have 1,500 miles of Gulf coastline. These are our waters & we will protect them," Iranian Foreign Minister Mohamed Javad Zarif said.

Iran has impounded the Stena Impero at its port of Bandar Abbas for allegedly breaking "international maritime rules".

The head of Iran's navy, Rear Admiral Hossein Khanzadi, said in an interview published on Tuesday that his forces use drones to closely observe "all enemy ships" going through the Gulf, "especially America's".

A US Navy ship may have brought down a second Iranian drone in the Strait of Hormuz last week, the head of US Central Command said in Washington on Tuesday.

The United States said that a navy ship had "destroyed" an Iranian drone in the Strait of Hormuz after the aircraft threatened the vessel, but Iran said it had no information about losing a drone.

"We are confident we brought down one drone, we may have brought down a second," General Kenneth McKenzie told CBS News in an interview.

AFP adds from Paris: French Foreign Minister Jean-Yves Le Drian held talks in Paris with a senior Iranian envoy, as France presses for diplomacy to overcome an upsurge in tensions with the Islamic Republic.

Le Drian told the French parliament he had met Deputy Foreign Minister Abbas Araghchi, who Iranian media said brought an unspecified message from President Hassan Rouhani for French counterpart Emmanuel Macron.

"We are now pushing Iran to return to the Vienna agreement," Le Drian said. "I met earlier with President Rouhani's special envoy to tell him that."

Paris has engaged in intense diplomacy to seek to solve the current escalation diplomatically, with Macron's foreign policy adviser Emmanuel Bonne twice visiting Tehran.

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