I beg your pardon but as Published in Al-Quds al-'Arabi on Febuary 23, 1998: Sheikh Usamah Bin-Muhammad Bin-Ladin: The ruling to kill the Americans and their allies--civilians and military--is an individual duty for every Muslim who can do it in any country in which it is possible to do it, in order to liberate the al-Aqsa Mosque and the holy mosque from their grip, and in order for their armies to move out of all the lands of Islam, defeated and unable to threaten any Muslim. This is in accordance with the words of Almighty God, "and fight the pagans all together as they fight you all together," and "fight them until there is no more tumult or oppression, and there prevail justice and faith in God."
We -- with God's help -- call on every Muslim who believes in God and wishes to be rewarded to comply with God's order to kill the Americans and plunder their money wherever and whenever they find it. We also call on Muslim ulema, leaders, youths, and soldiers to launch the raid on Satan's U.S. troops and the devil's supporters allying with them, and to displace those who are behind them so that they may learn a lesson.?
Granted that it was after the Khobar Towers but certainly the Iranian Mullahs voiced enough warning that we could have (and to a large extent did) expect to be attacked. We had plenty of warnings. Now Iran is no more explicit as to when or where an attack might come in this letter to Bush but it seems clear that they intend to strike.
See #224.