The UK will continue bombing Islamic State targets for "as long as it takes", Philip Hammond declared at the United Nations.
The Foreign Secretary told the UN General Assembly in New York that the people of Syria are facing the "twin evils" of IS and Bashar Assad's "murderous regime".
He addressed the gathering of world leaders and said they must work together to "crush" IS - also known as Isil - and "banish" it.
Mr Hammond described the chaos in Iraq and Syria as the "crucible of human civilisation" where "our collective values and our will to act are being most immediately challenged".
"We share a responsibility to act to end the bloody civil war and create an inclusive political process, and to work together to crush Isil and banish its ideology from the face of the earth," he added.
"The UK will continue to be a leading member of the international coalition against Isil, including carrying out more air strikes in Iraq than any other country except the US, for as long as it takes to prevail in what will ultimately be a generational struggle against the Islamist extremist ideology that drives it."
Mr Hammond praised the "extraordinary generosity" of Turkey, Lebanon and Jordan for their humanitarian efforts taking in Syrian refugees.
"It is incumbent upon all of us to support them as they bear that burden; to ensure that the UN appeals for Syria are fully funded.
"And I am proud that the UK is making the second largest contribution of any country to the humanitarian mission in the region.
"We judge it important we seek to support those who have been displaced as close as possible to their homes. Because there will be a new Syria to build and the country will need to draw on the talent of the Syrian people."
The fact that Mr Hammond delivered the UK's address to the UN's annual General Assembly, rather than the Prime Minister, has sparked accusations from Labour that David Cameron was failing to show leadership on Syria.