Asked by Yahoo News about US President Donald Trump's claim that extremists are hiding among refugees, Assad agreed, saying "you can find it on the net."
"Those terrorists in Syria holding machine guns or killing people, they are peaceful refugees in Europe or in the West," the Syrian leader said.
He did not specify how many of the 4.8 million Syrian refugees he meant, saying "you don't need a significant number to commit atrocities."
He also rejected Trump's plan to carve out safe zones for civilians in Syria.
The US president said last month that he "will absolutely do safe zones in Syria" for people displaced by the violence in a bid to reverse their migration to Europe and elsewhere. He did not provide details.
"Safe zones for the Syrians could only happen when you have stability and security. Where you don't have terrorists. Where you don't have flow and support of those terrorists by the neighboring countries or by Western countries," Assad said.
"It's not a realistic idea at all."
The White House last month ordered the Pentagon and State Department to draw up a plan to "provide safe areas in Syria and in the surrounding region."
The announcement came ahead of a surprise ban on refugees from Syria traveling to the United States, which a court has since suspended.
Other US politicians and officials have long supported the idea of safe zones in Syria, including Democrats such as Trump's presidential rival Hillary Clinton.
Critics say it would risk the US military becoming bogged down in Syria's civil war.
