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.