Those wanting sharia law in Britain are the "mirror image" of the British National Party (BNP) in seeking to draw lines between "them" and us", David Cameron has warned.
In a speech to local residents in Lozells, Birmingham, the Conservative leader warned that both the far-right party and Muslim extremists "seek out grievances to exploit", whether over race and faith, money or education and opportunity.
"The BNP pretend to be respectable. But their creed is pure hate. For the BNP, racism isn't a scourge, it's a political philosophy. They prey on voters who are disillusioned with mainstream politics," he said.
"And those who seek a sharia state, or special treatment and a separate law for British Muslims are, in many ways, the mirror image of the BNP. They also want to divide people into 'us' and 'them.' And they too seek out grievances to exploit."
Mr Cameron said people must be brought together, but - in a thinly veiled dig at Gordon Brown - insisted the government could not "bully" them into feeling British but must be encouraged by "building a Britain that every one of our citizens believes in".
"We must bring down the barriers in our country. We must push forward the frontiers of fairness. We must create equal opportunity, so everyone has the chance to get on in life," he argued.
The Tory leader's speech comes as a new survey for the Policy Exchange, a conservative-leaning think tank, finds more than a third of young Muslims would back sharia law in the UK, and 13 per cent supported organisations such as al-Qaida that fought the West.
Mr Cameron said he was shocked at the results, but said the issue was not about Islam specifically, but about wider barriers in society.
Unrestricted immigration was the cause of many problems, he argued, saying it put pressure on housing and public services and helped create "division, fear and resentment - among British people of all ethnic backgrounds".
He warned the government "needs to be in control of the situation" to ensure "proper integration" of all the different people coming in to the country, but warned that the policy of multiculturalism over the past 20 years had made this integration difficult.
"Multiculturalism has come to mean an approach which focuses on what divides us rather than what brings us together. It often treated ethnic or faith communities as monolithic blocks, rather than individual British citizens," Mr Cameron said.
Another major barrier to social cohesion was poverty, he argued, saying that "Not only is this an affront to social justice, it's also a breeding ground for resentment". He promised to make this issue a priority, in particular by improving education in deprived areas.