An old enmity.

Iran and the United States have been at loggerheads for 16 years, regularly accusing one another of terrorism and arrogance. But over the last few weeks, relations between the two have taken a decidedly nasty turn - moving away from a traditional trading of insults, toward more open confrontation.

The United States of America is under attack. On 26 June a truck bomb blew off the front of an American military installation in Al Khobar, Saudi Arabia, killing 19 servicemen and wounding 386. On 18 July, a TWA passenger jet exploded above the New York coastline. And on 26 July a pipe bomb marred that most prestigious of events, the Olympics, leading to a frenzy of speculation over possible terrorist involvement.

The rhetoric from the US establishment concerning terrorism has been prolific. The Clinton administration has been waging a high-profile diplomatic war against groups inimical to American interests world-wide for months, culminating in a G7 summit on 30 July almost entirely devoted to a US-defined terrorism. But these most recent attacks have knocked the stuffing out of US government statements reducing them to a mixture of wounded national pride and gung-ho bravura unparalleled since the Gulf War.

"We have to show them that we are rougher than they are," came the war cry from retired US Army General Norman Schwarzkopf, following the Al Khobar bombing.

Almost every statement made by US politicians since the start of the bombings has had Iran, implicitly or explicitly, as its focus. So far, the evidence is weak, but while Iran may yet be found responsible for these attacks, in many ways its involvement or otherwise is irrelevant.

Ways of linking Iran to the Al Khobar bombing do exist. The size of the explosive device is unusual for a domestic guerrilla attack, and of the two previously unknown organisations that have claimed responsibility, the Movement for Islamic Change and Hizbollah-Hejaz. The name Hizbollah if nothing else, can be directly linked to the Iranian-backed movement in Lebanon. The TWA explosion is another example of an unsubstantiated link. The first suggestion that Iran was involved came, according to US intelligence officials quoted by The Times, when an unnamed but. reliable exiled Iranian contacted the American embassy in Rome, saying the plane had been targeted by Iran.

The validity of this information is open to question, but its source is important. Recent Iranian successes in silencing its opponents (which the US regularly uses for intelligence gathering purposes, if not covert operations against the Iranian regime), have irked the US intelligence services, and given the US all the more reason for confronting Tehran, with or without firm proof of its involvement in more recent terrorist attacks.

In March this year, a mortar with a range of 700m was discovered aboard an Iranian ship by Belgian customs authorities. Members of the Iranian National Council of Resistance, based in Europe, say the mortar, and others like it being smuggled into Europe, were destined for use against Council leaders. That is not all.

In May last year, former Iranian Minister Reza Mazlouman was assassinated in Paris. A case is also underway in Germany in which one Iranian and three Lebanese are accused of the 1992 execution of three leaders of the anti-Tehran Kurdish Democratic Party of Iran (KDPI) in Berlin. An arrest warrant has even been issued for the current Iranian Intelligence Minister, Ali Fallahiyan.

On 23 July a journalist was sentenced to death in Tehran over an alleged plot to assassinate Iranian President Rafsanjani in 1994, and on the same day, three Iranians were executed for spying for Israel during the Iran-Iraq war.

The time-span between these events is long but they have been highlighted at a time when America is under threat, and needs to respond quickly if it is to appear in control. A link, any link, between Iran and attacks against US targets, or US-supported targets, is enough for the American intelligence and military machine to start salivating. And then there is Israel.

On 10 July, the new Israeli Prime Minister, Benyamin Netanyahu, warned the United States Congress that Iran was attempting to acquire nuclear weapons technology, and that it should do everything in its power to stop it.

While these allegations are not new, and have been supported (if not jointly fabricated) by US and Israeli intelligence services for several years, Netanyahu's speech brought yet more pressure to bear on the US to counter Iran. What is more, Netanyahu walked away from his visit to the US with an American pledge of assistance for two anti-ballistic missile systems aimed predominantly at intercepting Katyusha rocket attacks by Hizbollah from Israel's self-declared security zone in Lebanon.

The Al Khobar bomb and the TWA blast only days after Netanyahu's visit could have been directed at US support for Israel. On the other hand, Iran's links to Hizbollah in Lebanon are provocation enough for the White House already. Hizbollah attacks within the security zone over the last month have come with such ferocity and frequency that they have shown up weaknesses in Israel's northern shield. Deaths among Israeli Defence Force and Israeli proxy South Lebanese Army soldiers have been mounting, and it is Iran that is taking the blame.

The United States has been exploring two ways of reducing Iran's capacity to project itself beyond its borders, and recent events have been largely shaped by an existing American policy of economic disruption and military containment.

Since the destruction of Iraqi military might during the Gulf War, and the resulting lack of a regional counterbalance to Iran, the United States has had to redesign its policy toward Iran. This came in May 1993, when the Clinton administration came up with the Dual Containment Policy (DCP). The declared aims of the DCP were, and are, to use all available economic and military pressure to change the behaviour of Iran and uproot the Iraqi regime, in order to protect both the position of Israel in the region and the supply of oil to the West through the strategically vital Straits of Hormuz, the conduit for half the world's oil supply.

A series of economically wounding anti-Iranian laws have stemmed from the DCP. They include a June 1995 US embargo, which, having singularly failed to move America's allies behind it, led to Clinton's signing of a much tightened version amid the recent hysteria on 5 August. This latest law threatens sanctions on any company that invests more than $40 million annually in Iran.

Forty million dollars may sound like a very high threshold for investment before the US government acts. But it is a deliberate attempt to block the expansion of Iran's oil and gas sectors vital to the Iranian regime, if they are to pull themselves out of the economic morass they are in. Iran knew the law was coming, and it could have been a reason for a bombing.

Yet it is the presence of American servicemen in the Gulf that has created the most tension. It is of most immediate threat to Iran, and, as the importance of terrorism to the current dispute slowly fades, has become the major factor in the present stand-off.

As hopes for a local security arrangement between Arab states in the post-war Gulf receded, it became obvious that the United States war machine that had so flattened Iraq was going to stay. Iran had, not unreasonably, hoped to be a part of any new arrangements, but with its great enemy now patrolling close to its southern shoreline, that too became extremely unlikely.

When US forces went back into Kuwait after yet another tete a tete with Saddam Hussein in 1993, US military personnel levels in the Gulf reached an estimated 16,000. Over recent weeks, that figure has risen to 24,000 soldiers, airmen and seamen - in preparation for Operation Rugged Nautilus, a 60-day series of military exercises from bases in Qatar, Saudi Arabia and Bahrain, unquestionably a consequence of the DCP.

This military build-up bears no apparent relation, as yet, to the bombings. Yet it completes the logic of the confrontation between Iran and the US. The US fears Iranian interference in its oil supply and puts a military force in place to counter that possibility. Iran is understandably jittery at having so much enemy fire power so close to its territory, and might have instigated bombings in retaliation.

World opinion is not behind the United States. Many countries believe the Americans are overreacting to what is still only perceived threat. Iran cannot afford any kind of strike against its painfully rebuilt military machine, or its oil infrastructure. If no evidence of Iranian involvement in the recent bombings emerges, the US may baulk at seriously upsetting the status quo in the Gulf all by itself. But then again, 60 days is a long time in politics, particularly in the Gulf.