Five armed Iranian Revolutionary Guard boats have launched an unsuccessful attempt to seize a British oil tanker in the Gulf.

The tanker was entering the Strait of Hormuz, a strategic shipping route between Iran and the Arabian Peninsula, when it was approached by the Iranian vessels on Wednesday.

The Iranians ordered the tanker to stop in their territorial waters. The Royal Navy’s HMS Montrose, which was escorting the British ship, aimed its guns at the Iranian boats and warned them to move away, which they did.

The incident was filmed by a US aircraft overhead.

The British government confirmed the incident in a statement on Thursday.

“We are concerned by this action and continue to urge the Iranian authorities to de-escalate the situation in the region,” the US’s Associated Press reported it as saying.

Iran’s elite Revolutionary Guards rejected the claims. In a statement carried by the semi-official Fars news agency, they said their patrol boats were carrying out normal duties.

“In the past 24 hours there has been no encounter with foreign ships including English ships,” the statement said.

Wednesday’s incident came almost a week after British Royal Marines boarded an Iranian tanker, Grace 1, off Gibraltar and seized it on suspicion it was violating the European Union’s sanctions by shipping about 2 million barrels of crude oil to Syria.

BREAKING: UK government says 3 Iranian vessels unsuccessfully tried to stop British ship in the Strait of Hormuz.

— The Associated Press (@AP) July 11, 2019

The move sparked a diplomatic row between Britain and Iran, with Tehran summoning the British ambassador.

Earlier on Thursday, Iranian President Hassan Rouhani said Britain would face “consequences” over the seizure of the Iranian tanker.

An Iranian Revolutionary Guards commander added his own threats on Twitter:

“If Britain does not release the Iranian oil tanker, it is the authorities’ duty to seize a British oil tanker,” Mohsen Rezai wrote.

Tensions between Iran and the US and its allies have risen sharply since Washington stepped up economic sanctions against Iran and moved to bring the country’s oil exports to zero as part of a “maximum pressure” policy to make Iran halt actions that it said undermined regional security.

Iran has responded to the sanctions by starting to breach limits put on its nuclear activities under a 2015 deal with world powers.

Several oil tankers were attacked in waters near Iran’s southern coast in May and June, for which the US blamed Iran. Tehran has denied any involvement.

Last month, Iran shot down a US drone near the Strait of Hormuz, prompting US President Donald Trump to order retaliatory air strikes, only to call them off.

General Joseph Dunford, chairman of the US military’s Joint Chiefs of Staff, said on Tuesday the US was trying to build a military coalition to protect shipping in the region.

“We are engaging now with a number of countries to see if we can put together a coalition that would ensure freedom of navigation both in the Straits of Hormuz and the Bab el Mandab,” General Dunford said.

-with AAP