LONDON – Iranian ships attempted to obstruct a British-flagged commercial oil tanker as it sailed in the Persian Gulf, Britain's Defense Ministry said, a move that comes amid heightened tensions over a 2015 nuclear deal between Iran and world powers.

The Iranian vessels are suspected of belonging to Iran's Islamic Revolutionary Guard Corps. They were forced away from the oil tanker "British Heritage" after receiving verbal warnings from a British navy vessel accompanying the commercial vessel through the Strait of Hormuz – a strategically important choke point for oil delivery.

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

No shots were fired and the Iranian vessels heeded the "HMS Montrose"'s warnings.

Iran’s Revolutionary Guard Corps. denied the allegations.

The semi-official Fars news agency carried a statement from the Guard’s navy early Thursday saying "there were no clashes with alien boats, especially English boats."

"HMS Montrose" has since left the Persian Gulf, according to the ministry.

There was no immediate reaction from the U.S. Navy's 5th Fleet in Bahrain.

The incident follows a warning from Iran that it would retaliate against British interests after Royal Navy marines helped seize an Iranian oil tanker in the Mediterranean Sea last week allegedly on its way to Syria in breach of European Union sanctions. Iran said the seizure was illegal and that the supertanker was not headed to Syria.

"You, Britain, are the initiator of insecurity and you will realize the consequences later," Iran's President Hassan Rouhani said, referring to the presence of British warships in the Persian Gulf. The latest incident occurred near the island of Abu Musa.

Britain has sided with the United States in accusing Iran of attacking oil tankers in the Persian Gulf in June, a claim that Iran also denies. The attacks, along with Iran's shooting down of a U.S. drone, have roiled oil markets. About a quarter of the world's seaborne crude oil is transported through the Strait of Hormuz, a narrow passageway between Oman and Iran that connects the Persian Gulf with the Gulf of Oman and the Arabian Sea, according to the U.S. Energy Information Administration.

The United Nations' atomic watchdog confirmed Monday that Iran has started enriching uranium at levels that breach the nuclear agreement with world powers. It could spark new U.S. reaction over the deal the Trump administration abandoned a year ago and adds fresh pressure on France, Britain and Germany to salvage the accord.

The U.S. has been steadily reimposing sanctions that have damaged Iran's economy.

"Iran has long been secretly 'enriching,' in total violation of the terrible 150 Billion Dollar deal made by John Kerry and the Obama Administration. Remember, that deal was to expire in a short number of years. Sanctions will soon be increased, substantially!," Trump tweeted Wednesday, making inaccurate claims about the accord.

Iran has been permitted to enrich uranium at lower levels as part of the agreement, and is still doing so even with its recent jump to 4.5% enrichment, breaking the limit of 3.67%, according to the International Atomic Energy Agency. And there was no $150 billion deal with Iran, nor was it U.S. money. It was Iran's money, about $55 billion – for years frozen in international financial institutions – that was unlocked.

Dryad Global, a maritime security risk firm, said on Twitter that "British Heritage" was an oil tanker operated by British oil and gas multinational BP and registered in the Isle of Man. Lloyd’s List, a publication specializing in maritime affairs, said British-Dutch oil giant Shell had chartered the ship from BP. Lloyd’s List, said 20 British-flagged vessels have sailed through the Strait of Hormuz into Persian Gulf waters since July 2.

China and Russia, signatories to the nuclear deal alongside European nations, have called for U.S. and British restraint in the Persian Gulf amid elevated tensions with Iran.