TEHRAN, July 20 (AFP) - Questions in the United States over whether Iran played a role in the September 11, 2001 attacks highlight what many observers see as an ambiguous relationship between the Islamic republic and Al-Qaeda -- ideological rivals but with a common enemy.
President George W. Bush said Monday the United States was looking closely at Iran after the acting CIA chief said at least eight of the hijackers who carried out the attacks passed through Iran.
Iran has openly acknowledged some of Osama bin Laden's operatives could have passed through its territory, but insisted they would have done so "illegally".
"We have very long borders and it is impossible to totally control them," foreign ministry spokesman Hamid Reza Asefi said, comparing Iran's long desert frontier with Afghanistan to that between the United States and Mexico.
That, observers say, is entirely valid.
"Every year, thousands of Afghans and smugglers cross the border illegally," said a Tehran-based UN official familiar with border security issues. "It's a well-known fact Iran has trouble controlling its borders."
And as a foreign ministry source asserted to AFP, "some of the hijackers also studied in Germany and took flying lessons in the United States. So what if they also crossed Iran?"
In ideological and religious terms, Al-Qaeda and Iran's clerical regime may both be branded with the catch-all term "fundamentalist" but they are also worlds apart.
When operational in Afghanistan, bin Laden's fighters and his Taliban allies -- who adhered to a puritanical interpretation of Sunni Islam -- were well-known for viewing Shiite Muslims as low-lives, and massacring several thousand of them.
After the Taliban executed a group of Iranian diplomats in northern Afghanistan in 1998, Iran nearly invaded. The Islamic republic had already been engaged in running weapons and cash to anti-Taliban forces for several years.
Still today the word "Taliban" is used here as a political insult to epitomise village idiot ignorance. Iran even condemned the 2001 attacks, and cooperated extensively with the United States in setting up the Afghan government of Hamid Karzai.
That hardly suggests a backdrop for long-term cooperation, and even if both sides happen to hate the United States and Israel they also have their own unique reasons and mode of operation.
But suspicions have nevertheless emerged due to Iran's highly secretive handling of Al-Qaeda fugitives as well as an apparent bid to use them as bargaining chips.
In 2003, Iran confirmed it was holding senior Al-Qaeda members, but it has so far refused to identify them and says they could go on trial here.
As for the bulk of some 500 fugitives Iran said it detained in the wake of the US invasion of Afghanistan who were extradited, foreign diplomats involved in that process complained of "mixed signals", "last minute changes of plan" and "a lot of disinformation" on the part of Iran.
Diplomats and Arab press reports have pointed to the possible presence here of the movement's spokesman, Sulaiman Abu Ghaith, and its number three, Saif al-Adel, as well as Bin Laden's son and Al-Qaeda heir, Saad.
Iran has refused to comment, despite appeals from foreign governments who maintain the value of the information the captives hold declines as long as they are kept under wraps.
In other words, Iran at best stands accused of sitting on this intelligence gold mine rather than strike a potentially devastating blow in the US's war on terror.
This has sparked US allegations that the clerical regime is harbouring, and not cracking down on the movement -- with fingers pointing to more hardline military or intelligence elements in the regime outside central government control.
But acting CIA chief John McLaughlin has also said there is so far "no evidence that there is some sort of official sanction by the government of Iran" for the movements of the hijackers, nor proof of "some sort of official connection between Iran and 9/11".
Iran's government has fiercely dismissed allegations of a link, and on Tuesday powerful former president Akbar Hashemi Rafsanjani hit back by stating "everybody knows who made the Taliban and al-Qaeda".
Iranian officials have also responded by criticising what it sees as a failure by US troops in Iraq to crack down on the People's Mujahedeen, the main Iranian armed opposition group who were sheltered by Saddam Hussein.
A possible deal between Iran and the United States to reconcile this conflict reportedly broke down last year amid more of the mutual acrimony that has dogged their relations since the 1979 Islamic revolution here.
As with US allegations over Iran's nuclear energy programme -- seen by the US as being a cover for weapons development -- Washington appears to be lacking a "smoking gun", and Western diplomats here are far from convinced.
"It is my honest view that maybe, and that is a big maybe, some elements in Iran may have helped al-Qaeda," a senior Western diplomat here said. "But the same can be said for Pakistan and Saudi Arabia, and to a more serious degree."