The Beirut car bomb killed at least eight people, including Lebanese general Wissam al-Hassan of the Internal Security Forces (ISF), a well-known opponent of Assad.
"Everything indicates that this is an extension of the Syrian tragedy," Fabius told French television, claiming that it was "likely" Assad's regime was involved. "I wish to express how much we condemn this dreadful attack, how much we are in solidarity with the Lebanese people and government."
He called Assad a "manipulator" who wanted to spread the "contagion to Turkey, Jordan and Lebanon" and accused Lebanon's powerful Shia-Muslim movement Hezbollah, which is closely allied to Assad's regime, of involvement in the Syrian conflict.
"Hezbollah is in the Lebanese government and we don't see much of their role," he said. "But their presence in the conflict has been apparent in the past few days, such as the drone which overflew Israel."
A drone sent by Hezbollah managed to enter Israeli air space on 6 October before being shot down near a nuclear reactor.
Fabius said that Hezbollah, which is backed by Iran, wanted to "demonstrate more clearly" its support for Assad's regime, and said, "We cannot accept that."