(Adds quotes, colour)

DUBAI, Sept 7 (Reuters) - Al Qaeda leader Osama bin Laden said in a video issued ahead of the sixth anniversary of the Sept 11 attacks the United States was vulnerable despite its military and economic power.

It was not clear when the tape, acquired by Reuters Television from a web trawler in Europe, was made.

The authenticity of the tape could not be immediately verified, although bin Laden's image on an excerpt seen by Reuters matched a still photograph carried by an al Qaeda-linked Web site which had advertised the tape.

"Despite America being the greatest economic power and possessing the most powerful and modern military arsenal, and despite it spending on this war and its army more than the entire world spends on its armies and being the major state influencing the world's policies as if it has a monopoly on the unjust right of veto ... 19 young men were able ... to change the direction of its compass," bin Laden said in the tape.

"The subject of the mujahideen has become an inseparable part of the speech of your leader and the effects and signs are not hidden. Since the 11th, many of America's policies have come under the influence of the mujahideen."

The video shows bin Laden sitting at a table dressed in white and cream robes and wearing a white hat. Beneath him, a banner reads in English: "A message from Sheikh Osama bin Laden to the American people."

In it, bin Laden appears tired and sallow and his beard is much shorter and darker than in his last appearance in 2004, when he sported a long beard streaked with grey.

AlertNet news is provided by