Sabotage by an insider at a major utility facility, including a chemical or oil refinery, could provide al Qaeda with its best opportunity for the kind of massive Sept. 11 anniversary attack Osama bin Laden was planning, according to U.S. officials.

A new intelligence report from the Department of Homeland Security issued Tuesday, titled Insider Threat to Utilities, warns "violent extremists have, in fact, obtained insider positions," and that "outsiders have attempted to solicit utility-sector employees" for damaging physical and cyber attacks.