US top national security experts have released a report warning that America faces further attacks from al Qaeda. The report describes the threat as serious, ever-changing and expanding.

It's been nine years since the September 11th terrorist attacks - an immense human tragedy that Americans will never forget.

According to a report released on Friday, Americans still face a "serious and dangerous" threat from al-Qaeda, the terrorist group that masterminded the attacks.

The report by the non-partisan National Security Preparedness Group warns of the threat of more home-grown terrorists.

Bruce Hoffman, Terrorism Specialist, Georgetown University, said, "Today, America faces a dynamic threat that has diversified to a broad potential array of attacks from shooting to car bombs to simultaneous suicide attacks, to attempted in-flight bombings of passenger aircraft. And that this is a state of affairs, that as we approach the 9th anniversary of the September 11th attacks, is cause for concern."

The report has also found the US is still poorly prepared to deal with terrorist attacks.

It calls for greater involvement from state and local public security officials to prevent such attacks, while warning Americans about the danger of becoming too complacent.