In an essay published on a government website, the 82-year-old former Cuban president wrote that al-Qaeda "was born from the empire's own entrails," using "the empire" to refer to the United States, but failing to elaborate.
He said the terrorist group was "a typical example of an enemy that the hegemonic power dangles in a place of its choosing where it needs to justify its actions, as it has done throughout its history, fabricating enemies and attacks destined to strengthen its plans of domination."
The U.S. has used al-Qaeda as a pretext to carry out plans "outlined long before the attacks that brought down the Twin Towers on Sept. 11, 2001," Castro wrote.
Castro has previously accused the U.S. government of misleading the public about the Sept. 11 attacks, and his close friend and ally Venezuelan President Hugo Chavez says it is plausible that Washington was somehow involved in planning the attacks.
The U.S government says al-Qaeda chief Osama bin Laden masterminded the Sept. 11 attacks on the World Trade Center and the Pentagon.
The former Cuban president is suffering from a secret illness and has not been seen in public since undergoing emergency intestinal surgery in July 2006. His younger brother Raul took over as head of state in February.