U.S. intelligence officials believe that information indicating three terrorists may be plotting attacks on American soil on the anniversary of the 9/11 attacks "has serious teeth."

Reports say there is "credible evidence" of the plot's existence. A senior intelligence official told Investigative Project on Terrorism Executive Director Steven Emerson that two of the suspected terrorists live in the United States and that a third member of the plot operates out of Waziristan, in Pakistan's tribal area. One official stressed that the evidence for the suspected plot was "not confirmed but we are taking it very seriously given the specificity of the details we have collected."

Those details included information that a suicide truck bomb would be detonated on a major transportation venue in New York, Washington, Los Angeles or Chicago "in order to inflict as many casualties as possible."

It was also learned that five days after Osama bin Laden was killed, a group connected to al-Qaeda calling themselves "Soldiers of Allah" declared they would avenge the death of bin Laden and specifically cited the 10th anniversary of 9/11. U.S. officials say that there was no one specific "smoking gun" but that they "triaged" the intelligence from various sources including the materials scooped up from bin Laden's compound by the Navy SEALs. Since then, other information has been collected that pointed to a possible plot, but specific details emerged only in the last 48 hours. The official would not describe the nature of those details that resulted in the consensus by the intelligence and counter-terrorism communities that a specific plot was going to be launched on the 9-11 anniversary. Members of the House and Senate Intelligence committees and the congressional leadership were briefed early Thursday morning.