Iran's fast-attack craft, the type repeatedly used to harass ships in the Persian Gulf. Fars News Agency Photo via USNI News

Three Iranian gunboats failed in an attempt to seize a British oil tanker in Persian Gulf on Wednesday, a UK government spokesperson said to INSIDER.

A UK Royal Navy frigate was escorting the oil tanker and pointed its weapons on the Islamic Revolutionary Guard Corps vessels, CNN reported.

"We are concerned by this action and continue to urge the Iranian authorities to de-escalate the situation in the region," the UK spokesperson said.

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Three Iranian gunboats failed in an attempt to seize a British oil tanker in Persian Gulf on Wednesday, a UK government spokesperson said to INSIDER.

Islamic Revolutionary Guard Corps (IRGC) forces ordered a British oil tanker to alter its route in the Strait of Hormuz and tried to force it near Iranian-controlled waters, according to CNN, who first reported on the incident. But the HMS Montrose, a UK Royal Navy frigate, was escorting the oil tanker and pointed its weapons on the IRGC vessels.

The HMS Montrose verbally warned the Iranian forces, who then backed off. US aircraft observed and recorded the incident, according to CNN.

"Contrary to international law, three Iranian vessels attempted to impede the passage of a commercial vessel ... through the Strait of Hormuz," the spokesperson said to INSIDER, adding that the Royal Navy "was forced to position herself between the Iranian vessels and ... issue verbal warnings to the Iranian vessels, which then turned away."

"We are concerned by this action and continue to urge the Iranian authorities to de-escalate the situation in the region," the UK spokesperson said.

The incident follows increased tensions between Iran and the UK. On Wednesday, Iran threatened to seize UK tankers, which have recently been escorted by the HMS Montrose and a minehunter traveling through the Strait of Hormuz.

Iran's threats came after British Royal Marines seized an Iranian tanker suspected of violating the European Union's sanctions by shipping about 2 million barrels of crude oil to Syria.

"You [Britain] are the initiator of insecurity and you will realise the consequences later," Iranian President Hassan Rouhani said to a state-sponsored news agency on Wednesday.

"Now you are so hopeless that, when one of your tankers wants to move in the region, you have to bring your frigates because you are scared," Rouhani added. "Then why do you commit such acts? You should instead allow navigation to be safe."

The US Defense Department said it "was aware" of the reports and referred the matter to the Royal Navy. The Royal Navy did not immediately respond to a request for comment.

"We are aware of the reports of [the IRGC's] harassment and attempts to interfere with the passage of the UK-flagged merchant vessel British Heritage today near the Strait of Hormuz," Navy Capt. Bill Urban said to INSIDER.

"Threats to international freedom of navigation require an international solution," Urban added. "The world economy depends on the free flow of commerce, and it is incumbent on all nations to protect and preserve this lynchpin of global prosperity."

Iran denied it tried to seize the British tanker and said the claim was made by "American sources," the BBC quoted a state-sponsored media outlet as saying.

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