WASHINGTON (AP) ― President Barack Obama said Tuesday that a “lone wolf” terror attack in the U.S. is more likely than a major coordinated effort like the Sept. 11 attacks nearly a decade ago.

With the nation preparing to observe the 10th anniversary of hijacked airliners crashing in New York and Washington and along the Pennsylvania countryside, Obama said the government is in a state of heightened awareness.

“The biggest concern we have right now is not the launching of a major terrorist operation, although that risk is always there,” the president said in an interview with CNN.

“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,” he said.

“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.”

In Norway, Anders Behring Breivik, 32, was charged with killing 69 people last month at a youth camp. A lawyer for Breivik says his client believes the massacre was necessary to save Norway and Europe from Muslims and punish politicians who have embraced multiculturalism.

In recent years the U.S. has endured terror-linked attacks that authorities believe were carried out by a single person.

In November 2009, 13 people were killed at Fort Hood, Texas, in a shooting that led to charges against an Army psychiatrist who authorities allege had become an Islamic extremist.