WASHINGTON -- U.S. authorities may have thwarted another major attack. They're investigating a possible al Qaeda cell here in the U.S. which they believe was planning an attack against a subway or railway in New York City.
Authorities have broken up several homegrown terror cells since 9/11, but some say this one was the most dangerous yet.
None of the men currently under investigation in Queens, N.Y., and Denver, Colo., have been arrested or charged.
However, a source with knowledge of the situation told CBN News he believes the men have direct links to al Qaeda's leadership in Pakistan.
He also believes that they were part of the most serious al Qaeda threat against the U.S. homeland since 2006, when authorities stopped a plot by al Qaeda to blow up airliners traveling from Britain to the United States.
Authorities say Najibullah Zazi had recently traveled to Pakistan. It was his visit to New York City last weekend from Denver to meet with other members of the alleged cell that sparked anti-terror raids of several residences in Queens.
Zazi says he's innocent.
"I have nothing to do with al Qaeda - any link or anything with al Qaeda," he said.
Authorities did not find bomb-making materials in the New York raids, or in a search of Zazi's apartment outside Denver on Wednesday. But they reportedly did find maps, bomb-making documents, cell phones and 14 new brand new backpacks.
Suicide bombers in Madrid and London have used backpacks to carry explosives in recent years. Authorities believe this cell was looking to carry out a similar attack on the mass transit system in New York City.
"As recently as last year, the city was discussed as a potential target by ranking members of al-Qaeda," said NYPD Commissioner Ray Kelly.
Security has been beefed up at the city's rail and subway stations as the investigation continues.
Sources say the plot, while big, likely would not have caused carnage on the scale of 9/11.
But it has been eight years since al Qaeda carried out an attack on U.S. soil and some experts believe the group is anxious to strike again.