David Cameron has warned that the advance of Islamic State fighters could pose a threat to the safety of Britain's streets.
Mr Cameron said while it was not right to "send armies to fight or occupy", a firmer security response was needed to prevent the spread of "poisonous extremism in our country".
Mr Cameron said he feared the struggle against extremism would continue "for the rest of my political lifetime."
"This is a clear danger to Europe and to our security," David Cameron said in the Sunday Telegraph.
"The creation of an extremist caliphate in the heart of Iraq and extending into Syria is not a problem miles away from home. Nor is it a problem that should be defined by a war 10 years ago. It is our concern here and now.
"Because if we do not act to stem the onslaught of this exceptionally dangerous terrorist movement, it will only grow stronger until it can target us on the streets of Britain. We already know that it has the murderous intent."