“We will need to continue to fight against terrorism, wherever it rears its head, with renewed determination,” he said.
Now was “the time” for the Taliban to “break with” al-Qaeda and engage in a political dialogue in Afghanistan, he added.
In the long run, he said, it would be the Muslim people of the world who would “inflict the greatest defeat” on the ideology of Islamist extremism.
“Some wrongly thought that 9/11 was the expression of Muslim grievances. It was not,” he said.
“The true expression of what the people of the Muslim world want was seen in Tahrir Square in 2011, not at Ground Zero in 2001.”
Addressing the situation in North Africa and the Middle East, Mr Hague called on the international community to do more to help ensure the wave of the pro-democracy uprisings there are sustained and have a lasting legacy.
Urging the EU to offer “the hand of friendship” – and economic support – to countries embracing political reforms, he warned greater engagement could help prevent a “collapse back into more authoritarian regimes, conflict and increased terrorism”.