Al-Qaida continues to recruit Europeans because it's easier for them to enter the United States without a visa.
Director of National Intelligence Mike McConnell said European al-Qaida recruits in the border region of Pakistan are being trained to use commercially available substances to make explosives, and they may be able to carry out an attack on U.S. territory.
McConnell also said he worried that Osama bin Laden's recent video and audio releases may be a signal to terrorist cells to carry out operations, he told the Senate Judiciary Committee.
"That's unusual. He had been absent from airwaves over the last year. Our concern is that's a signal," McConnell said. "It just causes us to be concerned and vigilant."
Europeans are being recruited specifically because they generally do not need visas to enter the United States, he said.
"Purposely recruiting an operative from Europe gives them an extra edge into getting an operative, or two or three, into the country with the ability to carry out an attack that might be reminiscent of 9/11," he said.
McConnell's threat warning echoed what he told Congress in July at a time when he and the Bush administration were pressing Congress for swift passage of a new law designed to ease warrantless eavesdropping on overseas calls and e-mails.
McConnell warned then that the existing law which dictated when the government must obtain warrants from a secret intelligence court to eavesdrop had become a dangerous blockade to spying on terrorists overseas.
McConnell told the Senate panel Tuesday that half of "what we know" comes from electronic surveillance, and the outdated Foreign Intelligence Surveillance Act had degraded those intercepts by two-thirds.
Under the new law, the government can eavesdrop without a court order on communications conducted by a person reasonably believed to be outside the United States, even if an American is on one end of the conversation - so long as that American is not the intended focus or target of the surveillance.
Because of changes in technology, many more foreign communications now flow through the United States. The new law, called the Protect America Act, allows communications initiated outside the United States to be tapped without a court order when they pass through electronic channels on U.S. soil. That law expires in January.
The FISA law generally prohibited eavesdropping conducted inside the U.S., unless a court approved it.
In requesting the change, the Bush administration said technological advances in communications had created a dire gap in the ability to collect intelligence on terrorists, even those overseas.