WASHINGTON (CNN) -- U.S. vulnerability to al Qaeda-inspired extremism in Europe continues to be the key worry of the National Counterterrorism Center, the head of the agency told a Washington think tank Wednesday.
Michael Leiter says he is worried about complacency almost seven years after the 9/11 attacks.
"Violent extremism in Europe remains at the center of our concerns -- both for the danger it poses to our European allies and our interests, as well as the potential danger it poses to the United States," said NCTC Acting Director Michael Leiter.
The center is responsible for analyzing all terrorism intelligence.
Leiter cited as an example the 2006 thwarted plot to blow up American passenger planes flying from Britain to the United States.
Also, recently disrupted plots in Spain, Denmark and Germany had connections to al Qaeda and were, "at the very least inspired by [Osama] bin Laden's public call to wage war against the West," he said.
Although intelligence analysts indicate the United States does not face the same level of threat from al Qaeda that Europe does, Leiter said the nation "remains the top target for al Qaeda's operational planners."
Leiter called the handful of American homegrown plots "less sophisticated" than the ones in Europe. But he said he finds them troubling because they involved people who crossed ethnic and religious lines, unlike those overseas.
Leiter also expressed concern about al Qaeda expanding its global reach -- in particular to North Africa, where he said it has aligned with two terrorist groups. One of the groups is believed to be responsible for a suicide bombing two months ago in Algiers, Algeria, that killed nearly 70 people.
Although Leiter focused on the threat from al Qaeda, he pointed out that the Wednesday death of Hezbollah terrorist Imad Mughniyeh demonstrates there are other violent extremists who threaten the West.
He said he is worried about complacency 6 ˝ years after the September 11, 2001, terrorist attacks on New York and Washington.
"Every day that we move farther from 9/11 ... we run the risk of falling back into old and, I believe in this case, bad habits," Leiter said. He stressed the need for continuing cooperation among government agencies in fighting what he called a "long war."
The counterterrorism chief concluded his remarks by urging Americans to "continue to engage in a thoughtful, national debate on how this war and struggle should be fought so that we can, as a nation, take whatever measures are necessary for us to defeat a determined foe."
Leiter delivered his assessment at the Washington Institute, a think tank focused on Middle East issues. E-mail to a friend