IF we didn't know better, the natural assumption would be that America was in the midst of a full-scale war, the target of the biggest attack on its territory since Pearl Harbour. It had all the hallmarks of a military operation carried out by a vengeful state - pinpointing key objectives in a co-ordinated mission to cause maximum devastation.

So, it is all the more chilling to think that this bewildering level of destruction is the work, not of a powerful state with a grudge against the United States, but of terrorists, determined to cause havoc and send an unmistakable signal to the American people.

It is no surprise that the Middle East has been identified as one possible source of the perpetrators. America's role in the Israel-Palestine conflict has made it an object of hatred for extremists. But this leaping to conclusions has been proved wrong before, according to Dr Emma Murphy, lecturer in Middle Eastern politics at Durham University.

"When the Oklahoma bombing took place, everyone said it was Islamic terrorists. Until there is some kind of evidence of a Middle East link I would be reluctant to speculate," she says.

The then-biggest act of terrorism on American soil, when 168 people died in the Federal Building in Oklahoma in 1995, was later found to be the work of right-wing extremists inside the United States.

But there is no doubt that America has no friends among the more extreme groups in the Middle East, and that this situation has worsened since the election of George W Bush as president.

"Since his election, America has withdrawn from playing an active role in the Middle East peace process," says Dr Murphy. "At least under the Clinton administration, the United States was attempting to put pressure on Israel to negotiate, but George W Bush has pulled back and has let the Israelis do whatever they like.

"There is a very strong feeling that America is the power behind providing all the material for an Israeli government that is seen as engaging in war crimes, and America just lets it happen and pays for it."

American policy has been pro-Israel since the Second World War, the result of the strength of the Jewish lobby in domestic United States politics and a greater identification with what is seen as a western-style democracy, as opposed to an alien, Islamic world. Israel is seen as an ally in an otherwise hostile environment.

'The bullets that Israel is using to shoot the Palestinians have 'Made in the USA' on them, the tear gas comes from America, the aeroplanes and helicopters and the technology all comes from America," says Dr Murphy. "From a Palestinian point of view, America lies behind Israel."

United States Republicans have traditionally been isolationist and reluctant to get involved in overseas conflicts, and President Bush's decision to back away from the peace process, combined with the election of a right-wing government in Israel, has inflamed already burning resentment.

The Israeli government's activities in forcibly removing Palestinians from their homes, expanding Jewish settlements on occupied territory and restricting the Palestinians' ability to trade, have all added to the level of anger in the Middle East. The election of Ariel Sharon, seen as a war criminal by many Palestinians, as Israel's prime minister, has added to the fear that Israelis are turning away from peace.

"From the Palestinian perspective, they are in crisis and are at risk of becoming another nation of refugees. They believe there is no peace process and there is a right-wing government in Israel intent on destroying them," Dr Murphy says. "It is in that kind of environment that extremists thrive."

But this is not the only reason why America is regarded as an evil influence, adds Dr Murphy. "Palestine is just one aspect of a general Middle Eastern and Islamic resentment of American policy throughout the region. America is seen as intervening to advance its own interests, supporting corrupt and brutal regimes when it is in its interests to do so," she says. "It is seen as providing the military wherewithal to allow regimes to attack its own people.

"Although the vast majority of Arabs don't support terrorism, people like Osama Bin Laden are expressing a very real frustration that America is meddling in the Middle East."

Saudi millionaire Bin Laden is believed to be a major sponsor of terrorism and has close links to the Taliban regime in Afghanistan. He has so far survived several US attempts on his life, including cruise missile strikes on Afghanistan in 1998.

"It is perfectly possible that there is a link with what is going on in Afghanistan and the Bin Laden camp," says Pat Chilton, professor of politics and international relations at Sunderland University.

"It is partly a broader ideology - the Taliban are against the great evil in the world which they see in United States capitalism - but it has also become a very personalised thing with Bin Laden, and is closely tied in with Palestinian politics and America's protection of Israel. Bin Laden has built up a very personal crusade against the United States over the last ten years."

And for terrorists like Bin Laden, the worsening situation in Palestine provides a justification for striking hard at the United States.

'The official Palestinian line is very much against terrorism, but we know there are many factions within that camp and sometimes there is a co-ordinated approach with other terrorist groups," says Prof Chilton. "There are very strong links with other groups, both within the Middle Eastern region and internationally.

"I think with this scale of operation, we don't know of other terrorist groups that could carry it out. I think it is beyond the capacity of other groups, at least the ones we know about."

Terrorism on this scale would not only be beyond the capability of right-wing groups inside America, but would also not fit their pattern of attacking local targets, she says. "It is ideologically unbelievable for it to be an internal strike. To target the World Trade Centre and the Pentagon does not fit the pattern of that kind of internal terrorism. When one looks at the reasons why, it is going to be partly a kind of personal crusade and partly a coming together of a number of different groups that spring from different disgruntled communities across the Middle East. There is going to be quite a wide background to explain this kind of scale of action."

The danger is, she says, an atrocity of this magnitude will only bolster America's hard-line stance on the Middle East, instead of leading it to reconsider its role.

"The message is coming from the United States, absolutely consistently and very, very harshly, that they do not need to listen to anyone else. It ought to make people approach security in a different way and not simply to rely on Star Wars or other technical fixes. If people are prepared to sacrifice themselves, then no security measures can prevent disasters of this nature. The idea that you can tell people the United States will not stand for this, just doesn't hold water.

"It has been quite frightening over the last 12 months hearing the Bush administration saying that the United States doesn't want to know and doesn't need to respond, and will just take care of itself. The hope is they will begin to be a bit more responsive. Terrorism feeds on problems and those problems have to be addressed."