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.