The Obama administration is taking serious the still unconfirmed intelligence tip of a possible al-Qaida plot tied to the 10th anniversary of the Sept. 11 terrorist attacks, counterterrorism adviser John Brennan said Sunday.
The threat reported to authorities Wednesday night remains "specific and credible," Brennan said during interviews with "Fox News Sunday" and CBS' "Face the Nation."
"Again, it's not confirmed, but the president wants to make sure that we leave no stone unturned," he said. "And that's what the intelligence, law enforcement and homeland security communities are doing."
Investigators have chased a tip that al-Qaida may have sent three men to the U.S. on a mission to detonate a car bomb in either Washington or New York. But officials have said they've found no evidence al-Qaida has sneaked anyone into the country.
Brennan said officials are "looking at travel data, other types of pieces of information and trying to correlate them against that reporting that has come in."
"It's not confirmed but we are not relaxing at all," he said. "This is a 24/7, round-the-clock effort by all elements of the U.S. counterterrorism community both here in the United States as well as abroad."
The terror network has long sought to attack the U.S. again and several plots have previously been thwarted. U.S. Navy SEALs killed al-Qaida leader Osama bin Laden in a May raid at his compound in the Pakistani city of Abbottabad.
"This is something that we have seen before as far as al-Qaida's intent. We know that we acquired material from the bin Laden compound in Pakistan that he was looking at the 9/11 anniversary as a possible time to carry out an attack," Brennan said. "So there are elements of this report that are consistent with our knowledge of al-Qaida, but also there are also things here that are new and we are tracking down."
There was no immediate evidence that a powerful Taliban truck bomb that wounded 77 American soldiers and killed five Afghans outside a combat outpost Sunday was connected to the threat being investigated in the U.S., Brennan said.
The U.S. is continuing to work with Libyan rebel leaders to help officials there secure scores of shoulder-fired missiles and other weapons that have gone missing in the effort to oust fugitive leader Moammar Gadhafi, Brennan said.