"The crimes of the Syrian regime cannot go unpunished," Juppé said. "The day will come when the civilian and military authorities of this country will have to answer for their acts to justice.”
Juppé added that preparations should be started for the International Criminal Courtm ICC, to be seized.
Syria has not signed the international court's founding treaty so its prosecutors cannot investigate the conflict, where the UN says well over 7,500 people have died in the past year.
The court could only investigate the deaths and allegations of widespread human rights abuses if the case were referred by the Security Council. The council called in the ICC for Libya, but permanent members Russia and China now oppose strong international action on Syria.
On Monday, Russia's Foreign Minister Sergei Lavrov sharply criticised attempts to change Syria and Libya by "misleading" international opinion and "manipulating" the UN Security Council.
Without mentioning Western countries, Lavrov told the Council that unilateral sanctions, moves to "regime change" and encouraging the Syrian opposition were "risky recipes of geopolitical engineering which can only result in a spread of the conflict."
Meanwhile, the bodies of 47 women and children, some with their throats slit, were found in the restive Syrian city of Homs after a "massacre" that sent families fleeing the area, activists and the opposition said on Monday.
The discovery comes after UN-Arab League peace envoy Kofi Annan warned on Sunday that the situation in Syria had reached a "dangerous" level, as he failed to conclude a deal to end violence rocking the country during a weekend mission to Damascus.