Omar Bakri Muhammad is the founder of the U.K.-based terrorist group known as Al-Muhajiroun. "Kufr," roughly translated, is a denial or rejection of the truth and generally applies to non-believers.

Transcript:

OMB (Arabic):...unless we close our eyes, it is Islam and kufr at war. Islam is not at war with the West, Islam [is] at war with kufr....Whatever its name, whatever its called, [unintell] or communism, capitalism, all this ism and ism...

So my dear Muslim brother, 11th of September, if we want to assume bin Laden did it, it is part of the war between Islam and kufr.