"Their intentions are mass casualties larger than 9/11 inside the United States," Director of National Intelligence Mike McConnell said in an interview with the D.C. radio station WTOP. "A very large building. The Sears Tower, or some large building in Seattle or L.A. or Dallas."
McConnell also confirmed publicly what senior officials had told ABC News privately.
"In some cases they've got people positioned, more in Europe -- we suspect here in the United States, but we have no clear and compelling evidence they're in the United States," McConnell told WTOP.
ABCNews.com reported last week that senior law enforcement and intelligence officials had "multiple and credible" reports that an al Qaeda terror cell may be on its way to the United States or could already be in the country.
The Library Tower in Los Angeles has always been on al Qaeda's hit list.
In February 2006, ABC News reported that al Qaeda's original plan for 9/11 was to use a fifth jet to bring down the 73-story tower on the West Coast.
And as previously reported on the Blotter on ABCNews.com, 9/11 mastermind Khalid Sheikh Mohammed, in a written statement, admitted he was responsible for planning and financing a "second wave" of attacks targeting the Library Tower in Los Angeles, the Sears Tower in Chicago, the Plaza Bank in Washington state and the Empire State Building in New York.
Echoing the National Intelligence Estimate released earlier this week, McConnell said the safe haven al Qaeda enjoys in Pakistan has re-energized the terror group to pre-9/11 levels and said the group has stepped up its planning and training efforts for future attacks.
McConnell joins other officials, including Homeland Security Secretary Michael Chertoff, in voicing his concern of al Qaeda's threat against the U.S.
"We do worry about whether they are rebuilding their capabilities," Chertoff told the editorial board of the Chicago Tribune last week. "We strike at them; we degrade them; but they rebuild."