It was his first remarks on last week’s reported Israeli air strike in Syria.
Syrian TV has shown images of the raid Damascus says Israeli jets carried out on a military research centre in Jamraya last Wednesday.
US officials said the air strike targeted a weapons convoy bound for Lebanon. The Israeli defence minister has hinted his country was responsible.
Ehud Barak told a security conference in Germany on Sunday that the strike was “proof that when we say something we mean it”.
“We don’t think [Syria] should be allowed to bring advanced weapons systems into Lebanon,” he told the meeting of top international diplomats and defence officials.
President Assad said on Sunday that last Wednesday’s raid “unmasked the true role Israel is playing,
in collaboration with foreign enemy forces and their agents on Syrian soil,
to destabilise and weaken Syria”.