Obama: 'Lone wolf' attack is biggest concern

With the 10th anniversary of the September 11 attacks weeks away, President Obama said on Tuesday that he remains most concerned about a "lone wolf" attack on U.S. soil.

"The biggest concern we have right now is not the launching of a major terrorist operation, although that risk is always there, the risk that we're especially concerned over right now is the lone wolf terrorist, somebody with a single weapon being able to carry out wide-scale massacres of the sort that we saw in Norway recently," Obama said in an interview with CNN, referring to the recent attack on a youth camp outside of Oslo that left 77 dead.

While the United States has made significant progress in degrading al Qaeda's capabilities in recent years, intelligence officials have noted that the terror organization has increasingly focused on seeking U.S.-born collaborators to carry out attacks.

In 2010, U.S. citizen Faizal Shahzad was convicted after a botched attempt to blow up a car bomb in New York's Times Square.

In 2009, a U.S. Army officer was charged in an attack at Ft. Hood, Texas, that killed 13 and left 29 others wounded. Investigators learned that the officer charged in the shooting, Nidal Hasan, had communicated with Anwar al-Aulaqi, a U.S.-born al Qaeda operative who is based in Yemen, prior to the attack. More recently, an AWOL soldier, Naser Abdo, was charged in federal court with possession of an "unregistered destructive device'' that was allegedly to be used in an assault at Ft. Hood.

"You know, when you've got one person who is deranged or driven by a hateful ideology, they can do a lot of damage, and it's a lot harder to trace those lone wolf operators," Obama said.

Obama is scheduled to visit September 11 memorial sites in New York, Northern Virginia, and Shanksville, Pa., on the anniversary. Former President George W. Bush is scheduled to attend the ceremony at Ground Zero in New York with Obama on September 11.