The Leave campaign is being offensive to Muslims by painting Turkish people as "criminals and terrorists", the Prime Minister has warned.
David Cameron said the tactics of the Leave side, led by senior Tory colleagues Michael Gove and Boris Johnson, were "appalling".
"I do find it concerning the way that the Leave campaign are talking about Turkish people in this referendum.
"Some of the material they are putting out, painting Turkish people as criminals or terrorists, is frankly appalling.
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"Many British Muslims will be offended by the way they are trying to frighten people. I think it's a sign of desperation," Mr Cameron told The Muslim News.
Mr Cameron laid into claims by former London mayor Mr Johnson and Justice Secretary Mr Gove that Turkey could be a full member of the EU within four years.
"Any decision to enlarge the EU requires the unanimous agreement of all member states and their national parliaments. We all have a veto.
"France have already said they'd have a referendum before Turkey could ever join - and right now, 75% of French people are against that happening. Turkey has wanted to join the EU for decades. It is clearly not going to happen any time soon," Mr Cameron said.
The Prime Minister warned people not to believe Leave claims that more immigrants could come from the Commonwealth after Brexit.
"The Leave campaign are trying to tell people that leaving the EU would somehow allow for a massive increase in immigration from the Indian sub-continent. But the idea they would lobby for a big increase in non-EU migration if we were to leave the EU is ridiculous.
"It simply won't happen. They are basing their whole campaign on attacking migration - not on replacing European migration with migrants from South Asia.
"Does anyone believe the likes of Nigel Farage really want that?" Mr Cameron said.
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Writing for The Muslim News, Mr Johnson insisted Brexit would open the door for more Commonwealth migrants.
"I think it's fair that we shouldn't be straitjacketed into an immigration policy that favours a person based on where they were born geographically regardless of how much they want to contribute to society or what their skills are.
"So if we need the best and brightest talent then that talent should be able to come here from countries like India, Pakistan, Australia, or New Zealand. Immigration yes, uncontrolled immigration, no. We need to take back control of our borders.
"According to a recent ICM poll, 86% of British Muslims feel a strong sense of belonging to the UK - and quite right too.
"I love this country because it defines patriotism in a way that we can all embrace. The idea that being a so-called second-generation Briton, speaking more than one language, and having family and connections across the oceans, makes someone any less patriotic than someone able to trace their lineage back hundreds of years is simply absurd."
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