Britain is joining an American military campaign to blunt Iranian influence in Iraq and the Gulf.

In a move likely to heighten tension in an already volatile part of the world, US forces have been ordered to detain Iranian agents in Iraq and to strengthen substantially America’s military presence in the Gulf.

Two Royal Navy minehunters have arrived in the Gulf to reinforce a naval frigate on patrol in the area.

“We are going after their [Iran’s] networks in Iraq,” Zalmay Khalilzad, the outgoing US Ambassador to Baghdad, said. The aim was to change the behaviour of the Islamic regime in Tehran, he added.

Robert Gates, the US Defence Secretary, accused Tehran of “very negative behaviour”.

Twice in the past few weeks US forces have detained Iranian officials in Iraq, first in Baghdad and last week in the northern city of Arbil.

America has accused the Iranians of supporting militant Iraqi groups. Iran insists has insisted that all those detained were performing normal diplomatic duties. Although Mr Gates was recently an advocate of opening dialogue with Iran, as recommended by the Iraq Study Group, he told a Nato meeting yesterday that now is not the time to talk. Tehran’s behaviour justified America’s decision to beef up its presence.

“We are simply reaffirming that statement of the importance of the Gulf region to the United States and our determination to be an ongoing strong presence in the area for a long time into the future,” said Mr Gates.

The USS Dwight D. Eisenhower aircraft carrier group entered the Gulf in December.

It will be joined by the USS John C. Stennis carrier group. This is the first time since the invasion of Iraq four years ago that the US has deployed two carrier strike groups in the Gulf at one time.

In addition, President Bush has ordered the deployment of an air defence battalion equipped with Patriot missile batteries to protect America’s Gulf Arab allies from possible air attack from Iran.

Britain’s contribution is two minehunters HMS Blyth and HMS Ramsey, which will remain in the Gulf for an unusually-long two-year mission to keep shipping routes open in the event that Iran attempts to block oil exports.

The White House has insisted that it has no plans to take military action against Iran. But Condoleezza Rice, the US Secretary of State, described the build up as an evolving strategy to confront Iran’s “destabilising behaviour”.

Dr Ali Ansari, an Iranian expert at the University of St Andrews, said that the escalation could have serious consequences.

“There is a distinct possibility that the current cold war could turn hot,” he said. “This is an accidental war waiting to happen. Even with the best will in the world crises are not easily managed. Before you know it you can lose control of the situation.”

In spite of Iran’s defiant stand, there were reports yesterday that Tehran wanted to ease tensions with Washington. Ayatollah Ali Khamenei and President Ahmadinejad reportedly sent a letter to King Abdullah of Saudi Arabia asking him to relay a goodwill message to Dr Rice, who arrived in Riyadh last night.

The US military build-up is seen as an attempt by Washington to ease concerns among its traditional Arab allies in the region, like Saudi Arabia, Egypt and Jordan, whose leaders have spoken out repeatedly against the danger of Iran extending its influence across the Middle East.

The Iranians and their Shia Muslim allies are regarded as the main beneficiaries of the overthrow of Saddam Hussein in Iraq.

In Lebanon Iran’s proxy, Hezbollah, has emerged as the most powerful military force in the country. The Arab Gulf states are also concerned that Iran will try to foment unrest among their large Shia populations.

Of greater concern is Iran’s nuclear ambitions.

Yesterday Tehran announced that it was stepping up its uranium enrichment programme, which many fear could be a cover for producing highly enriched uranium, the fissile material needed to build an atomic bomb. Last month the United Nations Security Council called on Iran to halt its enrichment work and imposed limited sanctions against Tehran.

The Iranians said that they were pressing ahead with the programme and planned to have more than 3,000 centrifuges to enrich uranium at the heavily fortified plant at Natanz in central Iran. Referring to Iran’s refusal to accept repeated international calls to stop elements of its nuclear programme, Mr Gates said: “My view is that when the Iranians are prepared to play a constructive role in dealing with some of these problems, then there might be opportunities for engagement.”

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