But the waters are murky. Even after the plans were announced, there was confusion about which nations would be sending important resources such as warships to the Persian Gulf.

As tensions rise, the exact mandate remains uncertain, with two separate and possibly competing plans — one led by the United States and the other by Europe — under discussion.

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Meanwhile, Iran has rejected any need for Western ships to patrol the waters along its ­southern coast, instead pledging to secure the Strait of Hormuz itself.

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The prospect of warships patrolling the Persian Gulf is reminiscent of the “tanker wars” of the 1980s, when the U.S. Navy escorted commercial vessels from Kuwait traversing the Strait of Hormuz because of attacks on tankers by Iraq and Iran.

But this time, with potentially multiple missions at once, the situation could be more fluid.

What is the American plan?

The United States has said that it envisages a scheme whereby nations would protect ships that carry their own flag, but that joint operations would be designed to carry out surveillance on waterways. The plan, dubbed Operation Sentinel, has been under discussion for more than a month.

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Mark T. Esper, then the acting defense secretary, first called for a joint strategy to protect shipping in the Persian Gulf during a meeting at NATO headquarters in June. Esper was sworn in as defense secretary on Tuesday.

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On Wednesday, Esper said the United States will escort ­American-flagged ships facing threats from Iran “to the degree that the risk demands it,” but noted that the effort may not always involve U.S. military vessels.

Secretary of State Mike Pompeo said this week that the United States is “working diligently to build out a maritime security initiative” with “a broad range of countries participating.”

The State Department and the Defense Department held a discussion with allies about the idea on Friday. The meeting included more than 60 nations, according to a State Department spokeswoman who discussed the matter on the condition of anonymity per department rules.

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During a speech Tuesday, President Trump said the United States should not take too much responsibility for ships in the Persian Gulf, suggesting instead that “very rich” countries such as Japan and China could do it.

What is the European plan?

After a British tanker was captured Friday, Britain’s then foreign secretary, Jeremy Hunt, outlined a separate Europe-led plan Monday “to support safe passage of both crew and cargo in this vital region.”

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Speaking to British lawmakers Monday, Hunt said the plan is different from the U.S. proposal. “It will not be part of the U.S. maximum-pressure policy on Iran because we remain committed to preserving the Iran nuclear agreement,” he said.

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British officials have emphasized that the plan would be about ensuring freedom of navigation in the Persian Gulf — an aim that Tehran could theoretically support as well. But Mark Dubowitz, chief executive of the Foundation for the Defense of Democracies, a group that often calls for isolating Iran, said the European plan could ultimately count as a win for Trump.

“Burden-sharing from our allies gives them a stake in deterring and responding to aggression from the regime in Iran,” he said. “Since the majority of oil that moved through Hormuz goes to Asia and Europe, these countries have an even greater stake in preventing this aggression.”

Who backs the U.S. plan?

No nation has publicly pledged material support for the U.S.-led maritime security initiative. Experts say some countries may be concerned about being linked with the U.S. maximum-pressure campaign on Iran, either hoping to salvage the 2015 Iran nuclear agreement or because they still maintain good relations with Tehran.

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Jarrett Blanc, a senior fellow at the Carnegie Endowment for International Peace who also worked on the Iran deal at the State Department during the Obama administration, said the lack of traction was not surprising. “Other countries take the front line under U.S. command and control, but other countries do not trust us not to escalate [or] provoke,” he said of the U.S. proposal in an email.

Some nations that want good relations with both the United States and Iran have offered vague statements of support but have made no detailed commitments.

Following a visit from White House national security adviser John Bolton on Wednesday, South Korea’s presidential office said in a statement that South Korea and the United States “agreed to continue discussing ways to work together on the maritime security and freedom of sea navigation in the Strait of Hormuz.”

Who backs the European plan?

The British-led proposal has secured more backing, in part because European nations such as Britain, France and Germany, along with China and Russia, have remained in the nuclear agreement with Iran, even though Trump pulled the United States out last year.

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On Monday afternoon, German Foreign Minister Heiko Maas expressed public support for the British proposal, on the condition that diplomatic channels remain open. France issued its own message of support Tuesday.

“We are discussing with our U.K. and German partners, and several other interested partners, a European initiative to increase our knowledge of the situation at sea with the deployment of ­appropriate surveillance,” the French Foreign Ministry said in a statement. “This is to facilitate the safe passage of ships in the area.”

“As far as we are concerned, this initiative is intended to defuse tensions and facilitate de-escalation,” the statement added. “It differs from the U.S. approach of maximum pressure.”

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Some European nations may be cautious that Britain, amid a change in leadership, may draw back from its plans. Hunt was replaced as foreign secretary on Wednesday.

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But analysts consider the British proposal a clear indication that even in the final lead-up to Brexit, Britain is still opting to coordinate with its European partners on matters of security.

“To me, it’s a sign that the U.K. wants to stay closely aligned with Europeans on Iran policy,” said Ellie Geranmayeh, an Iran expert at the European Council on Foreign Relations.

It remains unclear what level of coordination there would be with the United States. “I think that would be a question for the U.S.,” said Alyson King, a British government spokeswoman based in Dubai.

How has Iran responded?

Both plans remain in the early stages. But there are already some signs of an increased international naval presence in the Persian Gulf.

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Maritime publication Lloyd’s List reported that a large British ship traveled through the Strait of Hormuz on Wednesday, shadowed by the British warship HMS Montrose. In a statement to the Associated Press, the ship’s owner expressed gratitude to “the U.K. and international community for their naval presence” in the area.

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But Iranian President Hassan Rouhani told a cabinet meeting Wednesday that it was Iran’s duty to protect the gulf and the Strait of Hormuz.

“I do believe that the whole world should be grateful to the Iranian Revolutionary Guard Corps for preserving security in the Persian Gulf,” he said, according to the Mehr News Agency.

What about the seized tankers?

Rouhani hinted that his country could release a British-flagged tanker, the Stena Impero, it seized Friday if British authorities let go of an Iranian tanker, Grace 1, captured off the coast of Gibraltar earlier this month.

The Iranian president’s proposal also came as the Swedish company that owns the Stena Impero said that it had made contact with the 23-member crew and that everyone on board was “safe.”

The Grace 1 tanker was boarded by Royal Marines on July 4 because it was suspected of transporting oil to Syria in violation of E.U. sanctions targeting Syria’s government.

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