At a trilateral meeting with Iran and Turkey, Mr Putin said Russia would continue its fight against “terrorists” in Idlib province.
Idlib is the Syrian opposition’s last major stronghold, with almost three million residents.
Syrian military forces, backed by Russia and Iran, are poised to launch a major offensive there soon.
The three-way meeting in Tehran had been seen by many as a final chance to prevent a large-scale battle in Idlib.
Syria has been in a civil war since 2011, after a peaceful uprising against President Bashar al-Assad turned into a conflict that has killed more than 350,000 people.-BBC/UNS