June 22, 2001: The United States Department of State issues a "worldwide caution" for U.S. citizens around the world of possible Osama bin Laden-related terrorist attacks. The warning is due to expire or be updated September 22.
June 28, 2001: Senator Warner states in his testimony before the Senate Armed Services Committee, that he would scrutinize their budget submissions "because we've got to prepare for an attack here at home of a terrorist nature in some form right in the cities here in the United States, and how best this nation responds."
July 20, 2001: The G8 summit in Genoa, Italy begins. Security is extremely tight because of large protests and intelligence indicating that terrorists associated with Osama bin Laden were planning to attack the summit to kill George W. Bush and other attendees. The reported attack plan involved crashing a plane packed with explosives into the buildings where the delegates were meeting or staying during the summit.
Numerous precautions against this attack were taken, including: George W. Bush staying at a separate location from the other delegates, fighter jets patrolling the sky over the city, a large no-fly zone for commercial aircraft, and surface-to-air missile batteries emplaced around the city.
August 6, 2001: George W. Bush is informed in his President's Daily Brief that Osama bin Laden was determined to strike targets within the United States and that the FBI believed activity consistent with preparations for hijacking US airplanes was underway.
August 18, 2001: The FBI reports that, if released, suspect Zacarias Moussaoui "might take control of an airplane and crash it into the World Trade Center".
September 9, 2001: Taliban assassination of Ahmed Shah Massoud, the military leader of the Northern Alliance Afghani opposition (he dies of the wounds on September 13).
September 10, 2001: The National Security Agency (NSA) of the United States intercepted two Arabic language messages to Saudi Arabia from Afghanistan. U.S. officals believed the two people in Afghanistan were connected with Al-Qaida. The statements "Tomorrow is zero hour" and "The match begins tomorrow" were contained in the messages. However, the messages which hinted at an impending attack, were not translated until September 12, 2001.
September 11, 2001: The attacks.
Exact dates unknown
In the months preceding September 11, the governments of at least four countries?Germany, Egypt, Russia and Israel?gave specific "urgent" warnings to the US of an impending terrorist attack, indicating that hijacked commercial aircraft might well be used to attack targets in the USA. [1], full list of July-August 2001 intelligence warnings here. The Egyptian and French warnings to the USA are said to have originated from Mossad and German intelligence. [2].
The exact dates these warnings were received is unknown, the warnings only being made public in the aftermath of 9/11.
German intelligence service BND told both US and Israeli intelligence agencies in June that Middle East terrorists were "planning to hijack commercial aircraft to use as weapons to attack important symbols of American and Israeli culture." (Source: Frankfurter Allgemeine Zeitung, September 14, 2001)
Egypt sent an urgent warning to the US June 13. It , Egyptian President Hosni Mubarak told the French newspaper Le Figaro that the warning was originally delivered just before the G-8 summit in Genoa, and was taken seriously enough that antiaircraft batteries were stationed around the Genoa airport. According to Mubarak, "an airplane stuffed with explosives" was mentioned. (Source: New York Times, September 26, 2001)
Russian intelligence notified the CIA during the summer that 25 terrorist pilots had been specifically training for suicide missions. In an interview September 15 with MSNBC, Russian President Vladimir Putin confirmed that he had ordered Russian intelligence in August to warn the US government "in the strongest possible terms" of imminent attacks on airports and government buildings. (Source: From The Wilderness web site; MSNBC).
The Israeli Mossad warned FBI and CIA in August that as many as 200 followers of Osama bin Laden were slipping into the country to prepare "a major assault on the United States." The advisory spoke of a "large-scale target," and The Los Angeles Times cites unnamed US officials confirming Mossad's warning had been received. (Source: Sunday Telegraph, September 16, 2001; Los Angeles Times, September 20, 2001)
The Independent, a liberal daily in Britain, published an article asserting the US government "was warned repeatedly that a devastating attack on the United States was on its way." The Independent cited an interview given by Osama bin Laden to a London-based Arabic-language newspaper, al-Quds al-Arabi, in late August. (Source: Independent, September 17, 2001)