By Jim Muir
BBC correspondent in Tehran
Iranian officials have dismissed allegations in the report of the 9/11 Commission of links between Iran and Osama Bin Laden's al-Qaeda movement.
The US inquiry said there was no sign Iran knew of the attack plans
A foreign ministry spokesman said some claims were US election propaganda.
Last week's report on the 11 September 2001 attacks stirred speculation about relations between Tehran and al-Qaeda.
It said there was evidence of contacts after the mid-1990s but no evidence of Iranian knowledge of, or involvement in, the plans to attack the US.
It did however suggest that, in advance of the attack, about eight of the hijackers left Afghanistan via Iran.
Asked about accusations of co-operation with al-Qaeda, the foreign ministry spokesman said that much of what was being said in the US at the moment was just election propaganda fodder.
He said attempts to prove links between Iran and al-Qaeda had failed - nobody believed them, he said, because of the deep ideological differences between the two.
At the height of al-Qaeda's involvement with the Taleban regime in Afghanistan, Iran nearly went to war with its eastern neighbour.
It frequently repeats the charge that it was the Americans who created al-Qaeda and the Taleban.
But Tehran has not denied the accusation that some of the al-Qaeda hijackers may have crossed Iranian territory.
It admits its border is long and hard to control, and compares it with the US' own border with Mexico.
Iran also says it has arrested and deported hundreds of al-Qaeda suspects.
It is continuing to hold an unspecified number of others including, it is believed, some senior figures. But it refuses to say who they are and it is resisting pressures to hand them over to the United States.