WASHINGTON - A decade after the 9/11 attacks, a "lone wolf terrorist" like the shooter in Norway now presents a bigger risk to the United States than a large-scale operation, President Barack Obama said on Tuesday.

"The most likely scenario that we have to guard against right now ends up being more of a lone wolf operation than a large, well-coordinated terrorist attack," Obama told CNN.

"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," he said.

Obama described "extraordinary progress" in degrading al Qaeda, the group behind the September 11, 2001 hijackings whose leader Osama bin Laden was killed by US forces in May.

"They are a much weaker organization with much less capability than they had just two or three years ago," he said, while stressing a need for "heightened awareness" of potential attacks around the anniversary next month.