Staffan de Mistura, the UN Special Envoy for Syria, is calling for a humanitarian corridor to free three million people trapped there.
The Syrian government - backed by its ally Russia - is vowing to go 'all the way' after groups they consider as terrorists.
Idlib is the largest remaining rebel stronghold. If Syrian government takes it, Damascus will claim the war is effectively over - and that it's won.
Al Jazeera’s Rory Challands reports from Moscow
