LONDON (AFP) - Ex-British leader Tony Blair, who played a key role in responding to the 9/11 attacks, said on Saturday terrorism remained a deep-rooted problem on the eve of the atrocity's 10th anniversary. Blair praised Western powers for reducing the terrorist threat but warned leaders should not let their guard down because of the death of Al-Qaeda chief Osama bin Laden, who masterminded the 2001 attacks on the United States. "I think we have certainly achieved significant results in fighting (terrorism). I think we have improved our security defences against the terrorists," he told BBC radio.