Both the US and Israel have been prime al-Qaeda targets in the past. It's even been purported by al-Qaeda that they used the US's support of Israel as one of the reasons for targeting the US. Despite it appearing that Israel would have no active role in 9/11 there are some connections, including; an Israeli spy ring of "art students" numbering potentially over 200 individuals. Several of these "students" have been suspected of being Mossad agents and have had military and intelligence experience(some said they were enrolled in a school that had no record of them while others said they attended the University of Jerusalem, which doesn't actually exist. I will cover some of these events regarding these "students" and the team that made up Gelatin and the "art project" The B Thing in an upcoming post, but I wanted to focus on the specific warnings from Israel to the US in the months before 9/11.

1. 8 - 8-15 - 2001: Israel warns of a "major attack on the US." Two Mossad agents travel to DC and meet with the CIA to tell them 50-200 terrorists have entered the US and are preparing a large scale attack that would leave many Americans vulnerable. Importantly, they add that there may be connections to Iraq. The CIA then says this meeting did not happen and the LA Times retracts the story, while other newspapers keep the article. (This could be one of the first times Iraq is mentioned to the public in regards to an upcoming terrorist attack, which will fit well with Bush's main goal of removing Hussein from Iraq and preserving their oil rights).

2. 8-23-2001: Mossad reportedly gives the CIA a list containing 19 names of alleged terrorists living in the US. Four of these names are known and they all will become 9/11 hijackers, including; Nawaf Alhazmi, Khalid Almihdhar, Marwan Alshehhi, and Mohamed Atta. This information is not treated as important by the CIA and they don't even share the list the FBI. This same day Alhazmi and Almihdhar are added to a terror watch list this day. No mention of the other 15 names of the list is known and Atta and Alshehhi are kept off the terror watch list.

3. 9-4-2001: Mossad sends another warning, however this warning is said to be somewhat vague and did not identify a target. This, however, should have increased the security of the state.

4. 9-11-2001 (2 hrs before the attack): Israeli employees at the instant messaging company Odigo receive warnings. The specific nature of these warnings was not released by Odigo. The Odigo headquarters was located 2 blocks from the WTC. The actual warnings were received in Herzliyya, Tell Aviv. Israeli security and the FBI were notified immediately after the attacks. Odigo has a feature that allows people with similar interests to connect. Odigo would then send the FBI the Internet address from the sender of the warnings. After 2 months the FBI reported it was still investigating. Nothing has been said of the incident from the FBI since.

Several other incidents involving Israelis including: the 5 dancing Israelis, the actions of Dominick Suter, Mossad agents being detained and released, Israeli surveillance of the Sears Tower, several Israelis being pulled over or stopped and explosives being detected and the theory that a vast Israeli spy network was literally monitoring and tracking the 9/11 terrorists will be looked at in post #3: Israeli connections to 9/11 (pre/post 9/11).

Edit: sources: The Terror Timeline (Thompson ppg. 306-308).