Assad, whose regime has been battling an uprising since March 2011, reiterated in an interview with official television Al-Ikhbariya his long-held claim that the roots of Syria's conflict lie in a foreign-backed conspiracy.
He also warned the conflict could spill over into Jordan, and that there would be no dialogue with the exiled opposition.
"The West has paid heavily for funding Al-Qaeda in its early stages in Afghanistan. Today it is doing the same in Syria, Libya and other places, and will pay a heavy price in the heart of Europe and the United States," Assad said.
Last week, the jihadist rebel group Al-Nusra Front pledged allegiance to Al-Qaeda chief Ayman al-Zawahiri, who had previously urged rebels to establish an Islamic state in Syria.
Comment: Despite the lack of information about how the suspects are implicated in the Marathon Day bombings, the police is keeping all residents of the area in a lock-down and a state of shock, while they patrol the streets fully armed and using the "bombing suspect" excuse to abuse anyone who they deem "suspect". Boston today is officially a Police Sate.
This video will give you an idea of the steps in this process. Watch it so that you know what comes next: