"The legitimate Syrian government has a right and must eventually take under control all of its national territory," Putin told Iran's Hassan Rouhani and Turkish leader Recep Tayyip Erdogan at the summit.
The Russian leader said it was important to begin work on a political settlement in Syria "as soon as possible" and urged Iran and Turkey to ramp up their coordination with Russia of their countries' foreign and defence ministries and security services.
Putin said "terrorist elements" continued to "stage provocations" and use drones in Idlib.
Russia discussing situation in Syria's Idlib with Iran and Turkey
"We cannot ignore this," the Russian president said. "We should solve this problem together."
The three leaders are expected to determine the future of Idlib amid growing fears of a humanitarian disaster.
The three countries are guarantors of the so-called Astana process, a track of talks launched after Russia's game-changing 2015 military intervention which has eclipsed the Western-backed Geneva negotiations led by the UN.
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