The Washington Post and The New York Times reported on Tuesday that officials were still analysing documents seized in July after a raid in Pakistan that showed al-Qaida surveillance of specific US targets.
Much of the information that resulted from an arrest in the raid was compiled before the 11 September 2001 attacks, The New York Times reported, citing intelligence and law enforcement officials.
Federal authorities said they were unsure whether al-Qaida's surveillance continued, the newspapers reported.
US State Department building in
Washington: security up
"You could say that the bulk of this information is old, but we know that al-Qaida collects, collects, collects until they're comfortable," a senior government official was quoted in the Times as saying.
"Only then do they carry out an operation. And there are signs that some of this may have been updated or may be more recent."
The Post cited officials as saying much of the information al-Qaida gathered on buildings in Washington, New York and Newark, New Jersey, was obtained through the internet or other "open sources" available to the general public, including floor plans.
"What we've uncovered is a collection operation as opposed to the launching of an attack," said a senior US official quoted by the Post.
American officials have previously warned of possible attacks before the presidential election in November.
"... we know that al-Qaida collects, collects, collects until they're comfortable"
Unnamed government official
The latest warnings were of al-Qaida threats to attack symbols of US financial might, such as the New York Stock Exchange, World Bank, and International Monetary Fund, among other targets in the New York area and Washington.
Documents, computers, surveillance reports and sketches were recovered in July after the capture in Pakistan of suspected al-Qaida computer expert Muhammad Naaim Nur Khan, also known as Abu Talha.