Terror threat “ongoing,” U.S. officials say

The tenth anniversary of the Sept. 11 terrorist attacks passed without any new attacks on U.S. targets, but security and counterterrorism officials say it’s too soon to let down their guard.

On Tuesday, Homeland Security Secretary Janet Napolitano and FBI Director Robert Mueller appeared before the U.S. Senate Homeland Security panel to discuss American vulnerability to terror threats 10 years after the Sept. 11 Al Qaeda attacks, Agence France-Presse reports. They said they were not yet ready to dismiss the intelligence that emerged last week indicating that two Al Qaeda operatives had traveled to the United States to carry out car bombings or other opportunistic attacks around Sept. 11.

(More from GlobalPost: D.C. and New York increase security due to car bomb threat)

"We consider it an ongoing threat," Napolitano told the Senate committee, CNN reports. "And we continue to lean forward into confirming that threat."

"Since we first had word of that threat, we have conducted hundreds of interviews, we have been pursuing a number of leads, and consequently – as a result of that – we've been able to eliminate some aspects where we thought that we ought to be looking in order to be able to determine if it was indeed a valid threat," Mueller said, according to Fox News. "But there's still work to be done."

According to CNN:

The FBI has conducted more than 300 interviews, and cleared all of those people of being involved in or knowing about a possible plot to attack the cities with vehicle-borne explosives or some other form of violence, a federal law enforcement official said Monday.

On Aug. 10, a senior U.S. official familiar with the intelligence told Fox News that trying to confirm the threat was "looking more and more like a goose chase."