Iran has denied charges that it has provided refuge for al Qaeda men fleeing Afghanistan. The US has announced that it will deal harshly with this if it true. The problem is, al Qaeda could have bribed their way to some kind of sanctuary in Iran. And then there is Iran's complicated political situation. The minority Islamic fundamentalists, who have veto power over the elected government, are already supporting terrorism. While the government opposes terrorism and al Qaeda, it risks civil war by trying to crack down on local Islamic radicals support for terrorism. The fundamentalists finance their operations from the 10-15 percent of the economy they control, assets acquired when the fundamentalists seized the property of the royal family (and their allies) after the 1979 revolution.) These assets are not taxed, but the government is trying to change that.
Meanwhile, the government is increasingly at odds with the judiciary, also controlled by the Islamic fundamentalists, which is prosecuting moderate legislators in secret trials. This is causing a growing popular uproar and pushes the country closer to civil war.