US intelligence officials have detected "enhanced activity" that points to a potential new attack against the United States or American interests abroad, according to a White House official.
The FBI also warned of a possible plot by Saudi-born militant Osama bin Laden's al Qaeda network to detonate bombs in apartment buildings in the United States.
The comments came as the New York Timesreported that US intelligence agencies have intercepted a series of messages among al Qaeda operatives indicating the group is attempting to launch an attack as big as or bigger than the one on September 11.
Quoting unidentified intelligence and law enforcement officials, the Timescharacterised the communications as "vague but disturbing." The intercepted messages are so general that they have left President George W. Bush and US counterterrorism officials uncertain about the timing, location or method in this potential attack, the Timesreported.
"There has been information of concern, enhanced activity of concern," the White House official, who asked not to be quoted by name. The information has been detected in recent weeks and months, the official said.
Officials cited by the Timessaid the intercepted messages represent some of the most credible intelligence gathered on al Qaeda's plans since the September 11th attacks.
The officials cited by the Timescompared the messages with the pattern of communications picked up in the spring and early summer of 2001, when al Qaeda operatives were detected speaking about a major operation.