In 2011, France helped arm the Libyan rebels who overthrew Moamer Kadhafi, but Paris fears the opposition in Syria is too divided to form a credible armed force and that the situation on the ground is too volatile.
"The Syrian people is deeply divided and if we give arms to a particular faction of the opposition we could trigger a civil war between Christians, Alawites, Sunnis and Shiites," Juppé warned, in a radio interview, adding "It could become an even bigger catastrophe than we have now."
For the past year, Assad's forces have been brutally repressing a revolt against his rule, firing on civilian demonstrations and residential districts as well as fighting a small and disorganised armed uprising.
Some Arab states, led by Saudi Arabia and Qatar, favour arming the rebels, but France and other Western powers still hope to secure a negotiated solution backed by a tough UN Security Council resolution condemning Assad.
Permanent Council members China and Russia have so far blocked attempts to agree a motion calling on Assad to stand down, a stance which Juppe said was based on a "bad medium term calculation" by Moscow.
"Russia criticises us for our intervention in Libya, accusing us of going beyond our mandate there, which I don't think we did," Juppé said.
"Russia has interests in Syria. It sells lots of weapons or it has sold lots of weapons to the Syrian regime. Russia also fears an Islamic contagion on its own territory, that's why it's against what's happening in Syria," he told listeners.