WASHINGTON (CNN) -- A former landlord of two of the September 11 hijackers was an FBI informant at the time, knowledgeable sources confirm to CNN.

The two hijackers, Khalid Almidhar and Nawaf Alhazmi, lived in San Diego in the fall of 2000 and were taken in by a Muslim man after he met them at a local Islamic center. The landlord had been an informant for the FBI, supplying information about the Islamic terrorist groups Hamas and Hezbollah.

The revelation, first reported by Newsweek, focuses renewed attention on possible mistakes made by U.S. law enforcement and intelligence prior to September 11. Newsweek reported that the FBI informant lived in close quarters with the two future hijackers.

"The FBI concedes that a San Diego case agent appears to have been at least aware that Saudi visitors were renting rooms in the informant's house," Newsweek reported.

Some members of the congressional committee investigating the intelligence failures and the September 11 attacks knew about the relationship between the landlord and the FBI, and the point will probably come up when the panel holds public hearings, expected later this month.

U.S. intelligence officials said that in January of 2000, when Almidhar and Alhazmi attended a meeting of known terrorists in Kuala Lumpur, Malaysia, that fact was communicated by the CIA to the FBI. Yet it was not until August 23, 2001, that the CIA warned the FBI and other law enforcement agencies to watch for the two men, and that they might try to enter the United States.

By that time, Almidhar and Alhazmi had been in the U.S. for more than 11 months.

The FBI contends the agency was never told about the two men before August 23 and says it can find no record of any such communication between CIA and FBI to show the information might have been overlooked. The FBI has maintained that position in its dealings with congressional investigators and has asked the CIA to document, if possible, having sent word earlier.

The San Diego landlord, reached by CNN on Monday, has refused comment.