The operation, masterminded by the country’s elite Revolutionary Guard, includes the construction of a high-tech spying post close to the point where Iranian forces kidnapped 15 British naval personnel in March.The move has forced British and American commanders to divert resources away from protecting oil platforms in the Gulf from terrorist attack and into countering the new Iranian threat.
The US military says that the spying post, build on the foundations of a crane platform sunk during the Iran-Iraq war, is equipped with radar, cameras and forward facing infra-red devices to track the movement of coalition naval forces and commercial shipping in the northern Arabian Gulf.
Commanders fear that one of the main purposes of the Iranian operation is to enable the Revolutionary Guard to intercept more coalition vessels moving through the disputed waters near the mouth of the Shatt al Arab waterway south of the Iraqi city of Basra.
The disastrous British handling of the hostage crisis has convinced some in the Iranian regime that there is mileage in further such attempts.
But the US military believes the listening post could also be used to help Iranian forces target commercial shipping in response to any US air strikes on its nuclear facilities.
Such operations would form part of their threat to launch guerrilla or asymmetric attacks on western interests if Iran is attacked.
US forces have responded by establishing their own listening post, positioning it on an oil platform just across the maritime border between Iraq and Iran from the Iranian position. The two spying posts are now monitoring each other’s activity.
British naval personnel who have recently served in the Gulf have told The Sunday Telegraph that tensions between the Americans and the Iranians have soared, with both sides heavily involved in espionage and counter-espionage operations.
British forces are also on high alert in an attempt to prevent any repeat of the March incident. “The Revolutionary Guard navy comes out every day to cruise around on their side of the line in their fast patrol boats and drop of supplies at their surveillance base,” one said.
“Every one is being very careful. The last thing anyone wants is for things to get out of control by mistake.
“The northern Gulf continues to be tense with the Americans and Iranians keeping a close eye on each other. Both sides sends out patrol boats to watch the other side and they have both set up bases packed with spy gear – loads of radars and cameras.”
British personnel said that Iranian activity had forced them to rethink their priorities in the Gulf: “Up to March, when our sailors were captured by the Iranians, coalition patrols concentrated on protecting Iraq’s oil export terminals from al-Qaeda suicide bombers.
"Now watching the Iranians is our top priority. We don’t want to be taken by surprise again and we need to keep know what they are doing in case things kick off if the Yanks bomb the Iranian nuclear sites.”
The Iranian spying post is located in shallow waters southeast of the tip of the Al Faw peninsular. It is located in water claimed by Iran, although the maritime boundary in the area is disputed by the Iraqi government.
In March 15 British sailors and marines - 14 men and one woman - were captured when their small craft were ambushed by a larger Iranian force of gunboats during a boarding operation at the mouth of the Shatt al Arab.
They were held for almost two weeks and accused of spying before being pardoned by President Mahmoud Ahmadinejad and deported back to the UK.
The subsequent fiasco over media deals to pay some of the sailors for their stories handed the Iranians a propaganda coup. British forces say the presence of the spying post has made it even more difficult to operate in the area.
“The Iranian surveillance base has been set up in a large naval crane that was sunk during the Iran-Iraq war. It is just across the boundary line and has a radar and night vision cameras to keep us under surveillance 24 hours a day.
"On our side of the line the Yanks have set up their surveillance base on a charted barge moored along side the Khawr Al Amaya oil terminal.
“The boundary line between Iraqi and Iranian waters runs only few hundred yards from the exclusion zone set up around the terminal and we have little choice but to send our people out close to Iranian waters.
"We are toe to toe with the Iranians here.
"The US Navy and the allies don’t venture out there unless they are all tooled up and have loads of boats in support. We are not taking any chances any more.”
The development is the latest sign of the growing tensions between the US and Iran, which Washington has accused of supporting attacks on its forces in Iraq.
With Iran last week announcing that it had achieved its goal of 3,000 centrifuges to enrich uranium for its nuclear programme, the prospect of US military action has increased.
Despite Iranian assurances that it is only seeking to develop a peaceful nuclear programme to meet its future power needs, the US believes it is intent on developing nuclear weapons.
Iran has warned that it will hit back if the US launches air strikes against its nuclear facilities and shipping in the Gulf would be expected to be high on its list of targets.
Iran has three submarines stationed at the Bandar Abbas naval base on the northern shore of the strategically crucial Strait of Hormuz, where the Gulf is at its narrowest, and these would be expected to play a significant role in any campaign against shipping.
A report in the respected Janes Defence Weekly magazine, published tomorrow, quotes coalition naval personnel in the region reporting regular patrols by Iranian Revolutionary Guards - the same force responsible for the capture of the British service personnel in March.
The Guards are reported to conduct regular patrols in small patrol craft and speed boats along the boundary of their territorial waters.
Regular Iranian naval forces, which include frigates and corvettes moored at Bandar Abbas, are considered more vulnerable to pre-emptive US strikes and there is less reliance on them in the northern Arabian Gulf.