The UK on Thursday accused Iran of attempting to obstruct a British oil tanker that was passing through the Strait of Hormuz a day earlier, partially confirming a previous report by CNN. The allegations were rejected by Tehran.

The latest incident came to light a day after Iran warned Britain of “consequences” over the detention of one of its tankers by the British Royal Marines off the coast of Gibraltar last week.

The UK government, in a statement on Thursday, claimed that three Iranian vessels unsuccessfully tried to hinder the British Heritage oil tanker. The Iranian vessels only turned away after receiving “verbal warnings” from a British Royal Navy warship.

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

Iran's Revolutionary Guards promptly rejected the allegations. “There were no clashes with alien boats, especially English boats,” the Guards said in a statement, which was published by the semi-official Fars news agency.

A CNN report earlier on Thursday had claimed that five Iranian armed boats confronted the British Heritage in the strategic Gulf waters. The Iranians ordered the tanker to change course and stop in Tehran's nearby waters, the report stated citing two U.S. officials.

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The Royal Navy frigate HMS Montrose, which is stationed in the neighboring Bahrain, came to the tanker's rescue according to CNN and Britain’s Daily Star newspaper.

"The UK maintains a long standing maritime presence in the Gulf. We are continuously monitoring the security situation there and are committed to maintaining freedom of navigation in accordance with international law," the British Ministry of Defense said in a statement.

The CNN, meanwhile, claimed that a U.S. military aircraft shot a video of the incident, which ended when the HMS Montrose – which was escorting the tanker – trained its guns on the boats and successfully warned them to back off. The video has not been released in public yet as the U.S. is still examining it to ascertain what exactly happened.

"Montrose is especially equipped with large canons on the deck to drive off small boats," CNN's Pentagon correspondent Barbara Starr remarked.

The British tabloid reported that the 4,900-ton warship carries a Wildcat helicopter and is bristling with weapons. The Type 23 frigate has a 4.5-inch gun on her bow and carries the powerful Sea Ceptor anti-air missiles.

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The alleged incident occurred hours after Iran's President Hassan Rouhani warned Britain of "consequences" over last week’s detention of its oil tanker Grace 1 off the coast of Gibraltar.

"I remind [this] to the Britons. You are the ones initiating insecurity, and will come to realize its consequences in the future," Rouhani was quoted as saying by Iran's Press TV.

The 330-meter tanker with a capacity of two million barrels, was stormed by British Royal Marines and Gibraltar port agencies on July 4 on suspicion of carrying oil to Syria in a likely violation of European Union sanctions against the Arab country.

An outraged Iran condemned the seizure as "maritime piracy" and summoned the British ambassador on three occasions to convey its protest at the "illegal interception." Iran claimed the destination wasn't Syria but "somewhere else."

Last weekend, a section of media reported the seizure of the British-flagged Pacific Voyager by Iran, which were also denied by Tehran as "fabricated reports."

"The tanker had to be checked on by UK officials over the weekend as she stopped close to Iranian waters – sparking fears she had been boarded," Daily Star reported.

The United Kingdom Maritime Trade Operations (UKMTO), which coordinates shipping in the Persian Gulf, said later that the ship was "safe and well." The UKMTO, had been in direct contact with the vessel, an official said.