Another potential attack 'remains very real'

New York City Mayor Michael Bloomberg (right) shows Defense Secretary Leon Panetta the National September 11 Memorial park on Tuesday.

NEW YORK -- After a decade of war with al-Qaida the potential for another devastating terror attack "remains very real," Defense Secretary Leon Panetta said Tuesday following a somber visit to ground zero of the Sept. 11 attacks on the World Trade Center.

The Pentagon chief walked through the National September 11 Memorial park and museum with Mayor Michael Bloomberg, and afterward told reporters that Americans must remain vigilant against the threat of another successful al-Qaida attack.

"The potential for that kind of attack remains very real," he said from the 10th floor of 7 World Trade Center, the first completed office tower at the site where hijacked commercial airliners were flown into the Twin Towers, killing more than 2,700 people.

Bad weather forced Panetta to scratch plans to visit Shanksville, Pa., where hijackers flew United Flight 93 into the ground, killing all 40 passengers and crew shortly after the coordinated terrorist attack began in New York.

Noting that many of al-Qaida's top leaders, including Osama bin Laden, have been captured or killed in recent months, Panetta said the nature of the terrorist threat has evolved to the point where al-Qaida "nodes" outside of Afghanistan and Pakistan are now the most dangerous.

"Yemen has risen to the top of the list," he said.

Panetta will attend 9/11 memorial events at the Pentagon on Sunday.