"We are relying on Russia to exercise very clear pressure on the regime which depends on it for survival," Macron said after a joint press conference with Russian President Vladimir Putin, Turkey's Recep Tayyip Erdogan and German Chancellor Angela Merkel.
Moscow is the principal ally of President Bashar al-Assad's government, which is fighting to recapture Idlib from rebel fighters.
The Istanbul summit came just a day after seven civilians were killed by Syrian regime fire in Idlib, according to the Syrian Observatory for Human Rights.
The leaders hailed "progress" following a deal last month between Syrian-regime ally Russia and rebel-backer Turkey to create a buffer zone around the north-western province and called for a lasting ceasefire in the region.
Their statement, read out by Erdogan, called for a committee to be established to draft Syria's post-war constitution before the end of the year, "paving the way for free and fair elections" in the war-torn country.
It also said there was "the need to ensure humanitarian organisations' rapid, safe and unhindered access throughout Syria and immediate humanitarian assistance to reach all people in need".
However Putin warned that if "radicals" were to "launch armed provocations from the Idlib zone, Russia reserves the right to give active assistance to the Syrian government in liquidating this source of terrorist threat".
Merkel said the leaders "have the duty to prevent another humanitarian disaster".
"The challenge is to end two wars: The war against terror and the war of the regime against large parts of its own population," she went on.
"A solution cannot happen through military means but only through political negotiations under the leadership of the United Nations."