The social policy think-tank Civitas criticises what it calls "hard" multiculturalists who insist that no culture is better than any other and that society should celebrate difference.
Its report says: "They simultaneously assert that no culture is better than another but they will happily elaborate that Western culture is actually inferior and shy away from celebrating it for fear of causing offence."
It added that no society could survive unless its members subscribed to a set of core values but that multiculturalists encourage minorities to see themselves as separate.
"The fruits of 30 years of state endorsed multiculturalism have been increased inter-racial tension and inter-racial sectarianism," the report, titled The Poverty of Multiculturalism, said.
"The fact that the London suicide bombers of July 7 and the would-be bombers of July 21 were born and bred in Britain – and encouraged by the state to be different – illustrates that hard multiculturalism has the capacity to be not only divisive but decidedly lethal."
The report has angered The Muslim Council of Britain which branded it as "speculative" and "unhelpful". A spokesman said: "Unfortunately one of the more regrettable developments since the July bombings is the way people on the right who were never supportive of multiculturalism seized on the bombings to undermine confidence in multiculturalism.
"These speculative comments are unhelpful and the best way forward in terms of finding out what happened is to hold a public inquiry and look into what happened and how to prevent such an atrocity in the future."
Ted Cantle, government adviser on racial integration, said that although multiculturalism had been blamed for a lot of things there was no evidence to suggest it had contributed to racial hatred.
Ann Cryer, Labour MP for Keighley, added: "Multiculturalism is a statement of fact – we have more than one culture. I can't agree that it can be blamed for the July 7 bombings."