What did US intelligence know before the 9/11 attacks?

The CIA have declassified documents showing US presidents were warned about Osama bin Laden and al-Qaeda before 9/11.

The significance of this report depends on the decisions, official reactions or confirmation that follow. The current assessment is initially based on reporting by Al Jazeera English.

Readers should distinguish established facts from initial claims. Practical consequences will become clearer through responses from authorities, markets or independent sources.

Watch for official statements, independent confirmation of the key details and updates to the original report.