Asked whether Europeans should fear refugees from Syria, Assad said: "It's a mixture. The majority, they are good Syrians, they are patriots... But of course you have infiltration of terrorists among them, that is true."
Czech Television said it had interviewed Assad in Damascus and would air the piece in full on Tuesday.
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Hundreds of thousands of Syrian refugees have reached Europe this year, often without documents, sparking fears in many countries that Islamic militants may be among them.
Islamic State's attack on Paris on Nov. 13 has heightened calls in the EU for more controls on people arriving.
Two of the Paris attackers had their fingerprints taken while travelling through Greece in October, a Paris prosecutor said.
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One was identified as Ahmad al-Mohammad from a Syrian passport found near his body, although it was not clear whether the passport was genuine or stolen.
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Turkey has promised to help stem the flow of migrants to Europe in return for cash, visas and renewed talks on joining the EU, in a deal struck on Sunday.
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