The Greek election result showed “an increase of extremes”, Juppé told Europe 1 radio, adding that that is “extremely worrying”.
Greece still had no government on Wednesday after the right-wing New Democracy failed to form one.
The left-wing anti-austerity movement Syriza, which at 52 seats became the second biggest party in parliament, was trying to pull together a coalition on Wednesday. The far-right Chryssi-Avyi (Golden Dawn) entered parliament for the first time, with 21 seats.
Syriza leader, Alexis Tsipras, said Tuesday that the election result “clearly nullified” Greece’s loan agreement, raising speculation that the country will leave the euro.
“The questioning of the treaties, which were painstakingly negotiated … risks sparking turbulence that will be difficult to control,” said Juppé, who went on to attend the last meeting of the outgoing cabinet of President Nicolas Sarkozy on Wednesday morning.
Incoming president François Hollande has called for a turn away from austerity in the eurozone but faces opposition from German Chancellor Angela Merkel.