David Cameron has rejected criticism of his decision to attack multi-culturalism, saying a "whole new way of thinking" was needed.
In a controversial speech on Saturday, the Prime Minister declared multi-culturalism a failure and called for a tougher approach in tackling Islamist extremism.
Shadow justice secretary Sadiq Khan responded by accusing Mr Cameron of "writing propaganda for the EDL (English Defence League)", while Muslim groups described the Prime Minister's words as "disappointing".
But Mr Cameron stood by his philosophy, telling the Sunday Telegraph: "You have to confront the extremism itself. You have to say to the people in Birmingham Central Mosque, or wherever, who are saying 9/11 is a Jewish conspiracy, that that is not an acceptable attitude to have.
"We don't tolerate racism in our society carried out by white people, we shouldn't tolerate extremism carried out by other people. It certainly means changing the practice, changing the groups you fund, the people you engage, the platforms you share with people, the people you let into the country. I think it needs a whole new way of thinking."
Speaking at a security conference in Germany with fellow world leaders, Mr Cameron said: "Frankly, we need a lot less of the passive tolerance of recent years and much more active, muscular liberalism. A passively tolerant society says to its citizens: as long as you obey the law, we will leave you alone. It stands neutral between different values.
"A genuinely liberal country does much more. It believes in certain values and actively promotes them - freedom of speech, freedom of worship, democracy, the rule of law, equal rights regardless of race, sex or sexuality.
"It says to its citizens: this is what defines us as a society, to belong here is to believe in these things. Each of us in our own countries must be unambiguous and hard-nosed about this defence of our liberty."
He said British society had been too cautious in standing up to "unacceptable views and practices" when they involve people who are not white and cited forced marriage as an example.
Mr Cameron's comments came as the anti-Muslim EDL held a major demonstration in Luton, prompting accusations that he was playing into the hands of the far-right. EDL leader Stephen Lennon reportedly said of Mr Cameron: "He's now saying what we're saying. He knows his base."