Iranian vessels are posing as US and British warships to interfere with oil tankers' GPS to send them off course, officials warned.

The Revolutionary Guard have reportedly been sending fake signals to coalition merchant vessels in a bid to send them mistakenly sailing into Iranian waters.

Iranian military forces then use this unwitting incursion into their territory as a ploy to seize the ships.

The US Department of Transportation's Maritime Administration issued the fresh warning to commercial shipping passing through the Strait of Hormuz and Persian Gulf.

A US defense official also told CNN that GPS jammers have been installed on Iran-controlled Abu Musa Island, which lies in the Persian Gulf close to the entrance of the Strait of Hormuz in order to disrupt the navigation systems of vessels and even planes.

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Iranian Revolutionary Guards drive speedboats at the port of Bandar Abbas where the Stena Impero was taken after it was seized

A helicopter hovers over British-flagged tanker Stena Impero near the strait of Hormuz as it was boarded by Iranian commandos

The US Maritime Administration warned that there have been reports of 'unknown entities falsely claiming to be US or coalition warships'.

It was also claimed that Iranian military boats have been sending fake signals to ships' Automatic Identification System (AIS) to disguise Iran's warship as commercial vessels.

During 'at least two' recent encounters with Iranian military forces ships discovered their GPS signals were receiving interference through 'spoofed bridge-to-bridge communications'.

When the British-flagged Stena Impero was seized last month by Iranian commandos it 'went dark' and switched off its radio transmitter after it made a sudden U-turn towards the Islamic Republic's waters.

Last week Iran seized the third foreign oil tanker in the space of a month, when it captured an Iraqi vessel it accused of 'smuggling'.

Commandos in black ski masks captured the Stena Impero in the world's most important waterway for oil shipments near the Strait of Hormuz on July 19.

Iranian Revolutionary Guard troops wearing ski masksare seen on board a helicopter flying over British-flagged tanker Stena Impero near the strait of Hormuz July 19

HMS Montrose (center) accompanying the Stena Important (left) and the Sea Ploeg vessels in the Gulf. Britain join forces with the US to protect merchant vessels in the Gulf amid heightened tension with Iran

The capture came two weeks after British forces seized an Iranian oil tanker near Gibraltar, accusing it of violating sanctions on Syria.

US Central Command, which oversees US military operations in the region, issued a statement last night saying: 'Vessels have reported GPS interference, bridge-to-bridge communications spoofing, and/or other communications jamming with little to no warning.

'Vessels have also reported spoofed bridge-to-bridge communications from unknown entities falsely claiming to be US or coalition warships.

'One vessel [Stena Impero] reportedly shut off its Automatic Identification System (AIS) before it was seized, complicating response efforts.

'The US remains committed to working with allies and regional partners to safeguard the freedom of navigation, the free flow of commerce, and the protection of US vessels and personnel in this region.'

But Iranian jammers have no effect on US military warships and aircraft, defense officials said.

Iran published footage on July 29 purportedly showing Revolutionary Guards warning off the British warship HMS Montrose during the seizure of the Impero.

A member of the Iranian Revolutionary Guards on board the tanker broadcast on Iran state TV

Iranian forces warned the British warship's crew against putting their 'life in danger' in the audio released on the country's state-run English language news channel, Press TV.

In a separate earlier incident Iran published an exchange during a failed attempt to capture the British Heritage oil tanker on July 10.

Amid the deepening tensions in the region the US and Britain dispatched warships to escort merchant vessels through the Gulf.

The United States has maintained a presence in the Persian Gulf for decades to ensure freedom of navigation and security of oil supplies.

But after recent seizures of shipping vessels, a flotilla of US Navy ships arrived in the Gulf last month.

On Boris Johnson's first full day as prime minister he ordered Royal Navy warships to escort British-flagged tankers along the vital waterway.

Two Royal Navy warships are currently in the region, the frigate HMS Montrose and the destroyer HMS Duncan.

Tensions have been escalating in the region for weeks, with US President Donald Trump last month calling off at the last minute an air strike on Iran over its downing of a US spy drone.

Six oil tankers have also been targeted in the Gulf of Oman in unclaimed acts of sabotage that the US blames on Iran, accusation Tehran has denied.

Iran recently began surpassing uranium enrichment limits set in the 2015 nuclear deal, which Trump withdrew from last year.