"The fact is that the war on Iraq, sought by the United States following (the) September 11 (2001 attacks), has not put an end to terrorism in the world," he told Italy's La Stampa newspaper.

"On the contrary, the result of this iron-fisted approach has been to give it a boost."

"It is now clear that terrorism must not be tackled through repression alone, but also through an understanding of its root causes," Blix told the daily, which is owned by Fiat industries.

"By waging unilateral preemptive war, the United States violated international principles to show its strength to the Islamic world after September 11, and by doing so has weakened the United Nations."

Iraq's alleged weapons of mass destruction -- the threat which formed the basis for the US decision to invade Iraq -- have yet to materialise despite intensive searches on the ground.

The United States had repeatedly argued that the alleged banned weapons risked finding their way into terrorist hands.