Russia and Turkey are in intense negotiations to ensure the rebel-held province of Idlib does not become a breaking point in their alliance on Syria, but the long term fate of the area still risks provoking a rupture, analysts say.
President Vladimir Putin and Turkish counterpart Recep Tayyip Erdogan have spearheaded an unlikely but so far sustained partnership to bring peace to Syria since late 2016, despite being in theory on opposite sides of the civil war.
The cooperation now faces its biggest test over Syria's northwestern province of Idlib, bordering Turkey, which Syrian President Bashar al-Assad wants to recapture to complete a string of military successes.
Idlib has over the last years become an increasingly densely-populated region where problems in resolving the seven-year Syrian civil war were effectively dumped to be resolved at a later date.
That moment is now drawing closer with expectations of a government offensive and fears over the combustible mix in the province of displaced people from other Syrian regions, moderate rebels and Islamist radicals.