Six years after the September 11 attacks in the United States, the "war on terror" is failing and instead fuelling an increase in support for extremist Islamist movements, a British think-tank said on Monday.

A report by the Oxford Research Group (ORG) said a "fundamental re-think is required" if the global terrorist network is to be rendered ineffective.

"If the al-Qaida movement is to be countered, then the roots of its support must be understood and systematically undercut," said Paul Rogers, the report's author and professor of global peace studies at Bradford University in northern England.