DUBAI — An oil tanker based in the United Arab Emirates is missing after it stopped in Iranian waters three days ago and switched off its transponder, raising concerns that it may have been seized by Iran amid heightened tensions in the Persian Gulf.

Shipping tracking data showed that the Panama-flagged Riah stopped transmitting its position late Saturday when it was off the coast of Iran’s Qeshm Island in the Strait of Hormuz, where Iran’s Islamic Revolutionary Guard Corps has a base.

Data showed that the ship was on its way to Sharjah in the United Arab Emirates before diverting sharply and slowing to a halt in Iranian territorial waters.

An Emirati official denied that the tanker has links to the UAE, saying that the ship is “neither UAE owned nor operated” and “does not carry Emirati personnel.”

It “did not emit a distress call,” said the official, who spoke on the condition of anonymity because he was not authorized to discuss the matter publicly. 

There were conflicting reports about the ownership of the Riah, a small oil-products tanker. But according to Equasis, a shipping industry database, it is operated by Prime Tankers LLC in Dubai.

A U.S. defense official, speaking on the condition of anonymity because of the sensitivity of the situation, said the U.S. military is aware of the disappearance and has no additional information to share at this time. The Riah did not request any help or put out any distress signal, the official said.

In Washington, Mark Esper, President Trump’s nominee to become his new defense secretary, said at a Senate confirmation hearing Tuesday that the U.S. military and allied forces have established Operation Sentinel to patrol the Persian Gulf region’s waters in response to recent acts by Iranian forces.

Since May, at least six vessels have been attacked near the Strait of Hormuz, the world’s most important oil choke point, in incidents that the United States has blamed on Iran. Britain said last week that Iranian naval forces attempted to block a British oil tanker traversing the strait but were repelled by a navy frigate escorting the ship. 

Esper said that if the British warship had not intervened, it probably would resulted in the Iranians assaulting the oil tanker or forcing it into Iranian waters and creating an international incident.

“Just a simple thing of appearing on the scene and the warship putting itself in between the IRGC boats and a merchant vessel was enough to deter something that could have escalated out of control,” he said.

Iran has denied involvement in the incidents but also threatened to retaliate against British shipping interests after an Iranian oil tanker was seized off the coast of Gibraltar earlier this month. 

The vessel, the Grace 1, was carrying 2.1 million barrels of light crude oil and was suspected of seeking to travel to the Syrian port of Baniyas in violation of European Union sanctions, authorities in Gibraltar said. Gibraltar is a British territory. 

“The vicious British government committed piracy and attacked our ship,” Iran’s supreme leader, Ayatollah Ali Khamenei, said in a speech Tuesday. Iran “will not leave such acts without a response,” he warned.

British Foreign Secretary Jeremy Hunt said Saturday that Britain would help facilitate the Grace 1’s release if Iran could provide guarantees that the ship’s cargo would not go to Syria. Iran has said that it is not subject to E.U. sanctions. 

The confrontation comes as Europe struggles to keep Iran in a nuclear deal it struck with world powers in 2015, following a U.S. withdrawal from the pact last year. 

The agreement curbed Iran’s nuclear activities in exchange for major sanctions relief, including from the United States. The Trump administration reimposed sanctions on Iran in the fall, prompting Tehran to scale back its own commitments under the deal. 

European nations have urged Iran to reverse recent moves to breach the agreement, including boosting uranium-enrichment levels beyond a limit set by the deal. Iran says it will continue to reduce its obligations to the pact in 60-day intervals until Europe compensates Tehran for economic losses suffered as a result of U.S. sanctions. 

Also Tuesday, Iran’s judiciary confirmed the arrest of French Iranian scholar  Fariba Adelkhah , the latest dual national to be detained by Iran ian security forces . French President Emmanuel Macron called on Tehran on Monday to explain why Adelkhah, 60, was arrested. 

“What has happened worries me a great deal,” Macron told reporters during a visit to Belgrade, Agence France-Presse reported. 

“I have expressed my disagreement and asked President [Hassan] Rouhani for clarification,” he said.

Dan Lamothe in Washington contributed to this report.