"In Gaza and in Israel, the absolute priority is a ceasefire," Laurent Fabius told reporters in Vienna, where he was gathering with his Western counterparts to discuss Iran's controversial nuclear programme in a meeting that was also due to touch on the Gaza offensive.
"In this context of an absolutely disastrous escalation, France -- like the UN Security Council -- calls for a return to the truce of 2012," he said, referring to a ceasefire agreement that ended the last round of fighting between Israel and Hamas militants in November 2012.
The latest descent into violence kicked off on June 12 when three Israeli teenagers were kidnapped and murdered, triggering a major military crackdown on Hamas in the West Bank and an escalation of rocket fire from Gaza.
The brutal revenge killing of a Palestinian teenager by Jewish extremists on July 2 added further fuel to the fire, which deteriorated into all-out conflict on July 8 when Israel launched an air campaign against Gaza militants.
The Palestinian death toll from Israel's punishing air campaign has hit 166, following the bloodiest day yet on Saturday when 56 people died.
So far, no Israelis have been killed, although militants in Gaza have pounded the south and centre of the country with some 660 rockets since the fighting began.
Israel has warned that preparations were under way for a possible ground incursion, with tanks and artillery massed along the border and some 33,000 reservists mobilised out of 40,000 approved by the cabinet.
A decision on whether to launch a ground operation could come on Sunday.
French President Francois Hollande also joined Fabius's calls for an "immediate ceasefire" on Sunday, pointing to the "increase in the number of Palestinian civilian victims" and the risks of ground intervention.
Defence Minister Jean-Yves Le Drian, meanwhile, called on "Israel to show restraint in its response and in particular, to respect international law and to ensure that civilian casualties are avoided."
"France calls for an immediate ceasefire... to ensure that every side starts talking to each other to avoid an escalation that would be tragic for this part of the world," he said in a televised interview.