DUBAI, United Arab Emirates — Iranian vessels in the Persian Gulf attempted to block a British tanker from traveling through the Strait of Hormuz, a key waterway for global oil shipments, Britain said today, in what appeared to be a major escalation in tensions between Iran and Western powers.

The tanker British Heritage was approaching the northern entrance to the strait when its British naval escort, the HMS Montrose, “was forced to position herself between the Iranian vessels” and the ship, a government statement said.

The navy ship issued “verbal warnings to the Iranian vessels, which then turned away,” it continued. “We are concerned by this action and continue to urge the Iranian authorities to de-escalate the situation in the region.”

Iran denied its forces challenged the British-flagged tanker, operated by the London-based oil and gas company BP. In a statement carried by Iranian news agencies, Iran’s Islamic Revolutionary Guard Corps said there had been no confrontations with foreign vessels in the past 24 hours.

The statement added that the Revolutionary Guard would “act with precision and power” if it received orders to seize any foreign ship in the area, the state-run Islamic Republic News Agency reported.

Iranian Foreign Minister Mohammad Javad Zarif said Britain was trying to “increase tensions” by saying the ship was unable to pass through the strait, calling the government’s claims “worthless.”

MarineTraffic, an open source vessel-tracking site, showed that the British Heritage traversed the strait overnight and was sailing through the Gulf of Oman.

The incident comes amid soaring tensions between Iran and the West, notably the United States and Britain. British forces last week seized an Iranian supertanker in the Mediterranean sea near the island of Gibraltar. The vessel, Grace 1, was carrying oil to Syria in violation of European Union sanctions, Britain said. Iran denounced the seizure as an “act of piracy” and vowed to retaliate against British shipping assets in the gulf.

“The enemy is going to regret this act,” Rear Adm. Ali Fadavi, a deputy Revolutionary Guard commander, said today, Iran’s Tasnim News Agency reported. “They would not have done it if they had done the minimum calculation.”

Fadavi added: “We had rented this ship, and we carried the cargo. Their action was very silly, and they will certainly regret it.” He also blamed the U.S. government for the seizure.

“Our reciprocal action will be announced,” he said.

Iranian Vice President Eshagh Jahangiri said today that the seizure of Iran’s tanker “was in violation of international laws,” the Mehr News Agency reported. Also attributing the seizure to both the United States and Britain, he added that “this act will bring disgrace upon them.”

In a speech at a conference of Iranian governors in Tehran, Jahangiri said, “They realized that Iran has found solutions to sell its oil, so they went too far, and ignoring international regulations, produced a spark which will embroil themselves.”

British Foreign Secretary Jeremy Hunt, a contender to succeed Theresa May as Conservative Party leader and prime minister, said the developments were “very concerning” but that he was “also very proud of the Royal Navy and the role they played in keeping British assets, British shipping, safe.”

“We are continuing to monitor the situation very, very carefully,” he told the BBC.

A spokesman for British Prime Minister Theresa May told reporters that Britain has a “long-standing maritime presence in the Persian Gulf. We are continuously monitoring the security situation there and are committed to maintaining freedom of navigation in accordance with international law.”

Tehran says it is responding to U.S. pressure following the Trump administration’s decision to abandon a nuclear deal with Iran last year. The 2015 pact curbed Iran’s nuclear energy activities in exchange for major sanctions relief, including from the United States.

The administration reimposed a near-total embargo on Iran’s economy in the fall. Since then, Iran has urged the other signatories — including European nations — to deliver the economic benefits promised to Tehran under the agreement.

This week Iran said it began enriching uranium beyond the limit set by the accord as part of a broader strategy to compel Europe to reset the terms of the deal. The United States on Wednesday accused Iran of “nuclear extortion” at an emergency meeting of the International Atomic Energy Agency, the United Nations watchdog that monitors Iran’s nuclear activities.

Zarif portrayed the meeting, which was called at the Trump administration’s request, as a failure for U.S. policy aimed at isolating Iran.

Britain, France and Germany have said they are committed to the nuclear agreement. They have also called on Iran to immediately halt its enrichment activities to preserve the deal.